Eh, if you like his policies, hope that he stays in and stays relevant as long as possible. November will not be won without Sanders supporters breaking for Hillary. Sanders supporters will not break for Hillary en masse without her showing support for the policies that matter to them.
I think the fear on the center-left is that Hillary needs as much time as possible to campaign against Trump. I don't agree with that. America already knows Hillary, intimately, and her polling numbers should be pretty consistent, for better or for worse. Whereas we are still having fruitful debate, sort of, on progressive issues here in the Democratic primary.