He has already been paid his 1 mil signing bonus. If he retires, I believe the Rangers can try to recoup that, but I doubt they would.
Escrow is capped at 20% this year and given the state of things, every player is going to lose 20% of their pay to escrow. So the 4.5 mil that Hank is still owed will become 3.6 mil. I don't know how much that is after taxes, but other players have given up as much or more, so can we please stop acting like there is no chance that a player who has already made 10s of millions of dollars in his career will retire and give up a few million?
Klein was owed 2.75 mil when he retired and, IIRC (CapFriendly doesn't have the contract details), Naslund was owed 4 mil. Klein hadn't made anywhere near as much as Hank, yet he gave up the money.
Like Dutch said, he has come back to NY, so he probably isn't thinking about retirement, but the money is probably on the lower end of the reasons why.