Some maybe do, but they're probably now like the dissident Priests were before the Tribunal disappeared.
Well, I believe most Dunmer in the mainland long for Vivec's return.
Aye, Vivec is the only living member of the Tribunal anyways and no matter who they worship, their ancestor gods for instance, they do have one of their own that became a GOD. So he always will hold a place in their hearts and prayers.
even though they went back to Worshipping Daedric Gods now, im sure it isnt a sin to worship them, if memory serves Vivec is considered a Saint in the Fourth Era (he could still possibly be aliveseeing as hes still an extremely powerful being even with most of the benifits of The Heart gone)