if a Trump vs Sanders election is looking likely, Michael Bloomburg will stand as an independent and presumably pitch himself as a sane middle-ground candidate.
Apart from the fact he essentially bought his way into office through sheer wealth (!), he was a very good NYC mayor. However, my concern would be that he would split the Democratic vote while Republicans recoil from his gun-hating, gay-hugging, cosmopolitan, “New York” (ie Jewish) values…and that leads to President Trump.
Much better is if Trump is not nominated, stands as an Indy and splits the (Cruz?) Republican vote. Then it will be full-on Nelson Muntz time.