Trump could still be liable under state criminal prosecutions, and the same set of facts can be tried under any jurisdiction that criminalizes them.
As an aside, the US has long had a "dual sovereignty" doctrine such that charging someone for the same crime at the federal and state levels doesn't count as double jeopardy - it's not considered "the same offense" in the 5th amendment sense. So even if Pence pardons Trump for, just for example, money laundering, the State of New York could still charge and try Trump for that same exact offense if it occurred within NY jurisdiction
1.
Even though SCOTUS recently reaffirmed that doctrine, do not be surprised if there's a challenge to it
if such a scenario comes to pass. I personally doubt such a scenario would happen (Trump manages to somehow surround himself with people ready, nay
eager, to take the fall for him, and frankly I'd rather his enablers burn than Trump himself). Trump has no filter, and he just says whatever pops into his head at that moment. I'd take his statement of leaving the country at less than face value.
The question of exactly what crimes he could be charged with is interesting, though. We
know there are all kinds of financial shenanigans at play, and I'm sure there's honest-to-God money laundering going through the White House itself. But beyond that, I don't know. Not a lawyer, don't play one on TV.
1. And convict. To quote from a Watergate-era Doonesbury strip, "It would be a disservice ... to prejudge the man, but everything known to date could lead one to conclude he's guilty! That's guilty! Guilty guilty GUILTY!!!"