Whether or not he "needs" to be a part of it, I don't think it would fly at all with the network or the backers without Barnabas.
I mean, to 99 percent of the population, DS WAS Barnabas Collins, full stop.
One reason why the show was canceled in the first place is that Frid no longer wanted to play Barnabas--or at least, did not want to play him as a vampire. I think Dan Curtis was ready to move on in any event but Frid's decision must have been a big factor in realize they'd reached the end of the line with it.
G.