Having the CAD not dis-engage cannot make you stuck in 4wd. The only problem a bad vacuum system can cause is not allowing you to go into 4wd.
If you can't get out, it's a T-case or linkage problem.
I would check the fluid. When mine was running low it wouldn't go out of 4wd. There's a plate to force it into 4wd when you pull the handle, but just a spring to push the fork out of 4wd. If it's not lubed up enough, the spring won't be able to kick it back.