Rahm would get little in the long run for betraying the president now. And Trump probably greases the palm of every mayor in a market that size.
Maybe Rahm cares more about money.
That said, it would be funny if Trump could grease Bloomberg, Bloomberg is worth significantly more then Trump, to the point that he could buy out Trump, lock, stock and barrel, and still be a billionaire (actually buy out a couple of Donald Trumps)......How do you pay off someone that could break you over his knee financially ? (not saying he didn't, saying it must be a funny scenario and a very high price).