Hi Stephen, while I'm not familiar with Pella, it sounds like an interesting problem.
So, are you saying the mechanism does not move internally? Is there part of the mechanism this is disconnected?
1.) My first guess would be marinate liberally with WD-40 and work the mechanicals as much as is practical to see if it will move.
2.) Try leaning on the door from both sides while you try to open it, in case there was expansion in the door or door frame.
3.) Disassembling the cover/trim hardware may get you to where you can jimmy the bolts back out of the strike plate.
4.) Call or email the Customer Service department of manufacturer of the lock and see if there's a remedy.