I think anyone can be replaced except for Mike and Chaz there's no other artists similar to them they are just UNIQUE
the other members can be replaced there are a lot of better drummers, guitar/bass players
it would be interesting to have a better bass player, Phi is just a lazy guy with his instrument he just follows the drums or the guitar he doesnt have his own rythms
and about who's the frontman.. Chester is the frontman for the media, Mike for the fans.