In the quest where Haer'dalis (the bard) opens up the portal in the theater, can you wait to go in and rescue the theater troupe? The average levels of character in my party is only 9 so thought I might want to wait, since you cannot leave.

Haer'dalis isn't worth rescuing.....but his friends are. :oP

IIRC, you can go back and do that quest when you feel more ready to do so. For roleplaying purposes, if you don't want to leave that portal open, simply delay giving Haer'dalis and Raelis Shai the stone that you got from that wizard's tower.

That is one hell of a wild quest!

There is no harm in delaying that quest until you are ready. Once you go through the portal my advice is do not step on the holes in the floor until you're whole party is ready to go through them.