Conventions of Space and Time - S4-E3
Continuity mistake: Annie splashes Jeff in the face with a drink and she asks for two more, with Jeff still having water dripping on his face. He shouts "enough!" and suddenly his face is much drier in the next shot.
Answer: The implication is that Jeff will still be teaching at Greendale after Annie and Abed leave. As for who became vice dean? It's never shown, since it's not really important to the series.
TedStixon