I’m really conflicted about this idea. On the one hand, I find the creativity in it very appealing. And I also like the motivation behind it – people whose life suddenly got complicated enough that they couldn’t refresh their stuff on time might end up losing everything, which really is sad.
Despite all that, I find myself unable to agree with the proposal. Let me try to explain why.
Before I start, let me explain that I don’t think the decay timer is a good mechanism. It can punish nice players unfairly and it rewards trolls, griefers and others who don’t fall into either of those two categories, but are still annoying in the way they treat shared spaces on the server 
So please don’t take the criticism of your idea as a defense of the decay timer – except in some later parts of my reply where I explicitly defend certain aspects of the timer.
To start off, I find that this proposal is basically the same as extending the decay timer from 1 week to 2 weeks, except with some added RNG. And while I find RNG to be a useful tool in a game designer’s toolbox, this is one of those occasions where I wouldn’t even reach for it.
Think about it this way: if they extend the timer to 2 weeks, at least you know that your stuff is safe for 2 weeks. If they implement your idea, the people who value their stuff are still required to refresh it at least once a week. In other words, why would I go away for more than a week without arranging for someone to refresh my stuff?
Of course, there’s another argument there: what if you didn’t arrange for anyone to refresh your stuff and you didn’t manage to come back in time to refresh it yourself? That’s where things get a bit trickier and we have to weigh different factors against each other.
Consider the cost first: this requires development effort that’s far from trivial. Apart from the necessary coding and QA (yes, I’m salty about QA), there are all sorts of unresolved questions here. When does this event take place? On reboot? At the exact time when this new timer ticks to one of its milestones? Or is it the way decay timer is handled: when a player comes into rendering distance and “activates” these buildings and placeables on the server, so the server plays “catch up” and applies everything that has to be done? Will it affect the performance and by how much? And so on.
Now consider the benefit: a certain minority of players will not lose everything. They should be a minority, because – let’s face it – having someone who can cover for you and refresh your stuff is one of the most useful aspects of PVE clans. There are other reasons to form a clan on a PVE(-C) server, but those can be worked around: sure, clan chat is nice, but many people already prefer Discord; sure, the Purge meter fills agonizingly slowly when you’re a one-person clan, but you can still make a Purge happen. Having someone other than you refresh your stuff? There’s no other solution for it except forming a clan.
In my mind, the cost outweighs the benefits by a significant margin, and that’s without even considering any other factors, such as what little positive effects the current decay system has.
Here comes the part where I present a tiny defense of a tiny slice of the current decay system. Again, please don’t take it as a defense of decay timer in general.
Like I mentioned earlier in my reply, there are certain PVE players that just aren’t “nice neighbors”. They could be outright griefers and trolls. They could be people who block up passages that don’t restrict resources, but force you to take a wide detour around a certain part of the map. They could be people who built a bunch of fugly foundation spam around their base so that nobody could build close to them.
Right now, the only hope anyone has of dealing with them is that they’ll be late to refresh their crap at some point. It’s a very, very slim hope that rests on a very, very slim chance, but at least it’s a non-zero chance 
Of course, I wish there was a better way. Which brings me to the reason why @Larathiel even mentioned me in this thread.
I’ll come out and say it plainly: I believe the PVE claim system is broken and needs to be fixed. I also believe it’s impossible to fix without introducing some kind of player-driven base destruction mechanic.
The problems I want to fix are:
- PVE griefing and trolling (e.g. walling in resources or other people’s bases)
- unreasonably massive builds (there was one forum post a while ago about a clan that controls 75% of the map)
- inactive players who just log in to refresh their buildings and do so indefinitely
(I’ll allow myself a slight digression here to defend that last point, because I know at least one forum poster who considers it a non-problem and thinks we’re all whining. A server is a shared resource. An official server is a public, shared resource. Anyone who builds a bunch of stuff and then stops playing indefinitely, except to keep their builds alive, is selfishly wasting “real estate” and, more importantly, server resources. All those builds do have an impact on server performance, too.)
One idea to fix that problem is what I’ve proposed on several other threads: an upkeep flag or pot. Place it on a building piece and it will consume fuel to protect that building piece and all the connected building pieces, by making them invulnerable to building damage. Make the fuel cost an exponential function of number of connected building pieces. Make the base cost depend on where you built: if there’s at least certain number (or fraction) of building pieces within a certain radius of certain spots like obelisks or Shattered Springs brimstone, it starts out much costlier than a normal base and gets fed into the same exponential function. Make it so each player can place only one upkeep pot, just like it works with bedrolls. Make the upkeep pot have a maximum inventory size. And then fine-tune the hell out of it.
Another idea I’ve had for a while is a declaration of war. To the best of my knowledge, I’ve never voiced this one before, because I haven’t sat down to think it through and I hate posting half-baked ideas. However, I’ll give it a try despite that. The idea is that a clan can unilaterally declare war on another clan. This would give the other clan a notification and a certain period of time to prepare (let’s say a day or two, this can all be discussed and tweaked). During the prep time, things are the same as without a war. Once the prep time expires, two things are suddenly in effect: 1) clan A can damage and destroy clan D’s buildings and followers, and 2) anyone can damage and destroy clan A’s buildings and followers. Additionally, this mechanism might be restricted to PVP hours. The war could either last indefinitely (until clan A ends it) or it can be capped by the server to a certain number of days (with or without an option for clan A to end it before that).
While neither of these ideas is designed specifically to help with your original goal of helping people take breaks without losing their stuff, I believe that fixing the PVE claim mechanism will still help them indirectly. The upkeep pot would allow them to pick a base they cherish the most and make sure it’s well taken care of. The clan war would make it so the decay timer can be bumped up to 14 or even 30 days without rewarding griefers and trolls.
I apologize for the huge wall of text and I hope it might be at least a tiny bit useful 
If there is any interest in discussing the upkeep pot or the clan war, I can always open a suggestion thread for them.