403(b) plan terminations....who must be 100% vested?

[Guest benefitsnewbie]

Hi, I was hoping someone could give me a quick rundown as to who must be 100% vested upon a 403(b) plan termination? Obviously those active employees will get accelerated vesting, but what about recently terminated participants who have no vesting, partial vesting? Any links to IRS publications would be greatly appreciated. Thanks a lot you guys!