So, what is the pont of the battle with Calder?

[Sermil]

At some point something is going to happen to allow team evil to get past the defenses and put the heroes on the run again.

I think the fight with Calder will be the instigation of it.
Too early to guess how, but maybe he'll chose to runaway (he clearly won't surrender again) and smash through the walls? Trigger some other defense? Blow stuff up?
Do something near the threads of creation that would put a serious dent in the place?

Or just escape, run into Redcloak, and tell him he's falling for a shell game, and tell him how to bypass it.