I read that Mustaine wanted something to happen, but Ellefson bailed several tines and never gave an answer, so Mustaine moved on.
Regardless, the people that want Ellefson back are holding on to the glimmer of hope that they'll put something like PSBWB or Rust in Peace together. These are the same people that are holding out hope for Metallica and listen to the hype they leak every time they record another album that "The new album will be a return to their roots".
Instead of pulling for bands from the past doing something of substance now, give some press and interest to bands that have been creative consistent, but have not gotten the notariety. I was tired waiting around for more of the same old shit and bands I liked going commercial, so I just searched out new bands that deserved my $$$.