If I use a pass do recordings stay unlocked after it is over or if my plan expires?
Yep! As long as you recorded with an active paid pass or subscription, those recordings get Slopes Premium forever. Oh, and as a bonus while you have an active subscription any activities you didn't have an active pass for in the past get unlocked for free.
This doesn't apply to recordings that were recorded while on the free trial if you don't upgrade to a paid subscription when the free trial ends. In that case, once the free trial ends, those recordings will lose Slopes Premium.