Nothing has been stated about access to the battle tower, your servants or the contents of the chest there. There is no reason to not keep what is in your inventory (especially since you can get a bunch of unique stuff in the arena), and you would at least need comparable services to your platforms. I can see having the battle tower NPCs escaping an attack and bringing essential equipment with them, just to move everything to Aleroth, but wouldn't expect to simply be cut off from the battle tower.