If they put him away for the rest of his life (which they might), he may regret that diet.
In his plea deal, which still has weight and validity, he also plead guilty to state level crimes.
If Trump pardons him, it can only be for federal crimes. They would just keep him locked up until he could be sentenced for state level crimes. Even if Gamble v USA prevails, they cannot get double jeopardy for tax evasion. Mueller would probably have some other crimes added. He's screwed.
A lot of people are howling "stupid ass - he should have copped a deal!!". An interesting fact came out tonight: Cohen stopped short of full cooperation too. Contrary to Cohen's stated reason - to allow him to be sentenced earlier, I suspect they both did it for the same reason: the judge might be lenient on a number of transgressions but his limits would be really tested if these two were traitors (as it appears they were). That's probably why they've been as harsh with Cohen as they've been. Cohen and Manafort appear to have put their own greed ahead of their country and that's probably worse to most Americans than anything Richard Nixon and his clowns did (ignoring that most didn't know he scuttled Vietnam peace behind the scenes to get elected). This paragraph is partly conjecture on my part but I think that I have reasonable foundation. I think that missing part in these documents might be the most damning.
If and when folks join those dots, they will not let Mueller's work be dismissed. These people may deserve gallows consideration.