Lets hope he sings like a canary
It won't matter. Trump will say he barely knew him and he was irrelevant and possibly made coffee for everyone and his base and the right nut media will soak it in and believe him. No matter who and no matter the position and the evidence of role and involvement. Not forgetting, Trump saying they are great people. His MO is to distance them and make them nobody's once they leave their position.
They will then go out of their way to make the guys life hell ( not that it can't get much worse for him) and that of his family's.
If he does sing it needs to be something solid and concrete that can prosecute people. Otherwise he is another in a long line.