Looking at polls, Kasich is likely out soon. He isn't consistent enough to unseat Rubio as establishment guy. Carson/Cruz aren't going anywhere because they don't give a crap about what the party wants. Carson will either have to start winning or run out of money though.
People that think Rubio is in trouble don't understand the Republican's unpledged delegates. With those all likely to go with the establishment guy, current counts are basically:
Trump: 67
Rubio: 447
Cruz: 11