If Trump was able to replace Ginsburg, Kennedy, Breyer and Thomas, you should have 6 solid conservatives, 2 liberals and wonky Roberts. In that scenario I think Roberts would drop all pretence and reveal himself to be a total liberal. Alito would be the oldest of the conservatives which would (barring an unforeseen death) secure the conservative majority for at least 20 years.
I knew going into the last election I would probably hate half of what Trump would do in office, but it was obvious his Supreme Court picks trumped all other concerns.