As far as I am concerned, anybody could get up on the stage, sing with Eddie and Alex and it wouldn't matter. They really don't even need a singer, but that's just me.

Van Halen is working with David Lee Roth right now on a new album and a tour.  Sammy Hagar is still working on a Chickenfoot project but says that he would work with Van Halen again.  He said that it is not in the works, but he would.

 When it went sour, it wasn't just because of us. There was a lot of outside forces. Our manager died and a new guy came in, and he just totally divided the band and conquered us, you know?!," he continues. So I think there will come a time where Eddie's gonna wake up and go, 'Hey, man, I miss being friends with Sammy,' if nothing else, or, 'I would love to make that music again, or play those songs again.' 'Cause they have no choice — they've got Sam or they've got Dave; they can't find a new guy — they already tried that and it didn't work. So it's inevitable.

(quote from www.rockaaa.com )