First of all, you have my sympathy to that misfortune incident. Some players experience things that others do not and this makes things more difficult. I never lost a thrall undermase, I never lost a thrall this way that you did, I never lost a thrall from elevator great fall, yet too many others did. It is not the first complaint I hear about thrall killed in bizarre ways. So again you have my sympathy on this. It is tiresome and frustrating to loose rare thralls this way.
Heads up exile
No matter if you hit the misfortune jackpot. I can assure you that in the past I have lost hundreds of thralls or pets, by poisoning, by lava, pvp, stone stacking etc… but most of them was from game mechanics and only a few from “wrong game mechanics”. By now I get used to it, my thralls never carry special equipment, or “expensive” equipment. The game mechanics provide us the heavy epic cimmerian steel armor that focus on vitality which is the far more important attribute for thralls, almost free of cost. Thralls do not need their armor to be repaired or their weapons too. So instead of dismantling these armor pieces to get literally nothing, farm them and dress your thralls in purges or when they follow you. This way you will reduce a lot the cost of loss. Sword of Crom is “necessary” only in a few boss fights it this game, for all the other fights even the star metal great sword with an upgrade is more than enough for a thrall to defend and crush all the others. Cimmerian bersekers spawn with this sword out of the wheel of pain and they have main spawns in each map. So all you loose here is a weapon upgrade, literally nothing again.
Playing pvp, especially in official servers be prepared to loose everything and when I say everything I mean everything. All you have to do is experience a raid of, or a God attack, or a spawn killer camping etc… Several times I exit warmakers dungeon in pvp servers, after 2 hours of farming scraps and died before I exit the loading screen 

. This is official pvp
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It was me, my own fault on this one, nobody else’s.
However… What doesn’t kill you makes you stronger they say…
It’s true.
If you want to continue playing solo pvp, I would suggest you to join a private server. Official servers is just a simple model of how servers can be, free of charge, but with too many mistakes. Private servers are almost perfect for pvp and a really good admin (there are a lot) can make your gaming experience awesome. Not to mention that if something like this would happen to a private server the admin would recover your loss at once… or the next day, but surely your loss will be recovered
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Once again, heads up exile, move forward, this belongs to the past now 