What was the point of this expedition if the Empire attacked and wiped everyone out?
In the latter case, Tais would have survived too.
It was difficult to combine two tasks anyway.
At another time during the journey, Erephir says:
-- Oh, when we return, I'll create all sorts of powerful, beautiful, and indestructible things for you and for myself, and then we'll have a completely different conversation, guys. It's a pity, of course, about some things, but what can you do if Her Highness has taken care of a forge and good materials (so that it's better than in Tais!)... Maybe there will even be some cosmic ore? In short, we will become stronger than before, don't worry. I just need to eat a lot of OD and maybe some blacksmithing potions so that I can create an artifact right away from under the hammer.