So I was about to get the developer version of PlayBook 2.0, but then I want to know, if I lose my Apps, after I upgrade my PB to the official OS 2.0, and that If i upgrade my PB to OS 2.0 Developer version, will I be able to upgrade to the offcial one, and do i keep my apps.
Short answer, no. Your apps are tied to your Blackberry ID (at least any that you've bought through App World). And your machine likely won't wipe anyway.
If you've sideloaded any converted Android apps, and you wind up wiping, you should be able to reload.
Otherwise, there IS no new "developer preview". OS 2 will be the only version out there for a fair while.