Here's what I said when he cast the deciding vote against repealing the ACA:
I'm as surprised as you guys are, but I guess I can Monday morning quarterback it as a result of his obsession with his legacy, which has got to be stronger now than it's ever been. If this is the last chapter of his biography, "shows up fresh from brain tumor surgery, gives a rousing speech, and then does one last maverick face turn and rescues the legacy of the man he fought so bitterly against" makes for a perfect Hollywood ending. When they make the movie, they'll play it up like Senator Paine changing his vote and Darth Vader saving Luke from the Emperor all rolled into one.
(The movie will not include McCain then endorsing Trump's tax cuts despite their being forced through under exactly the same budget reconciliation process he had so vocally opposed months earlier.)