I really think thralls / pets should take no fall damage, since they randomly teleport to their deaths if you jump down from any kind of height or even go anywhere near the edge. I also believe that they should, if possible, take X damage per second while in lava vs immediately dying. I’ve built bridges in the volcano but even with them, thralls will randomly plop off of them to their deaths. This makes thralls and pets entirely useless anywhere near lava.
Combining these two things makes me personally never ever take either with me anywhere. With the new thrall HP compared to a players HP you could even make the damage something like 500 per tick to still pretty much instakill a player while giving thralls a chance to get out before dying to bad pathing.