I think it depends what Gates says...Gates could implicate Manafort to the level where he has to speak now or Manafort could continue to look at 25-30 years and accept his fate of life behind bars. I think Manafort is going to try to play the long game as long as he can
His long game is a pardon. But a pardon is strategic, Trump has to know or have some type of idea what Mueller has before he can pardon Manafort. Otherwise pardoning Manafort leads to an admission of guilt and if Mueller has information or SIGINT of Manafort conspiring or emailing Trump about a crime - he will play himself.
They're nervous because nobody has the slightest idea what information Mueller has or what he knows - it's his Ace in the hole. Hell, half the people who pled out may or may not have been talking through the wire. No one knows.
Mueller isn't showing his cards anytime soon, he has until at least mid-terms to start making major moves. Can Manafort hold up financially until then? Can he maintain his sanity on house arrest until then? Who else is going to get indicted before then? What else is going to leak? Too many variables.
This isn't a easy call for Manafort, he's doing a lot of thinking right now. Because we all know, even if he keeps his mouth shut, the KGB/FSB doesn't believe in loose ends.