Can I long rest before the final(?) area of act 2?

Hi! So I just stormed Moonrise towers. I had cleared out the dungeons so it was a pretty easy fight and all the npcs of the inn survived too!

So I go up and fight ketheric, he goes down, but not before the undead situation went a little haywire.

And now there’s some weird fleshy rift in a tower. Jaheira just joined my team. I’m guessing I’m supposed to just jump into the weird tower. And both my shadowheart and my sorcerer tav are low on spell slots.

Can I long rest before going after Ketheric? Does that progress something like him regaining his invulnerability? I’m not sure how much healing and how many spells I’ll need. Should I just try to keep going like this? Thanks!