Are Tony Hale and and Jeffory Tambor the main problems for season 5?
Tony Hale is very busy with veep which is also why he was hardly in season 4 and tambor has started out in the very popular Transparent.
all the others would probably be fine.
Will arnett has a movie coming out next year and had some netflix show (not sure if it's being brought back
Jason bateman appears in the odd movie.
Cera the same, but less so in recent years
David cross does the odd show and does stand up tours
while the actress for Lucille, Lindsey and maebe dont' seem to be doing that much at all