[microbet]

If he had pushed, when would 99 be a good call?

If his pushing range were 66+, A7+ it is just barely not a call by ICM. Anything looser and it is a good call to his push. So, if you think that is his range it is probably a good push because of whatever tiny FE you have.

From what you are saying it sounds like his hand range is considerably wider, which would make it a clear push reraise.

That doesn't rule out a call, but a call seems bad too me since he would never fold post flop if he hit anything and you couldn't fold post flop either. But I suppose it could give you a chance to push him off a draw of just overcards.