Well if the Warden is romancing Zevran and takes the ultimate sacrifice, then the epilogue screen says that he ultimately does take over the Crows. I did a War Table mission when we were going after some Antivan noble and the crows offered to work with us, then Zevran stepped in and offered to work for us instead. So at that point he was still messing with them and we had to smuggle him out of the area after he had taken their mark, so clearly he's not in a position to take over just yet.
Mind you, in another of my play throughs he is off in the west reunited with my Warden, so given the variables, including the possibility that he may already be dead, I don't think they'll ever have him actually taking the Crows over, just continuing as a free agent.