Depends on two key questions:
(1) will manafort cut a last minute deal?
(2) will Trump pardon him?
Either could easily happen, and I sort of expect that (2) is more likely. If neither of those things happens we'll see some really weird shit though, because evidence at trial has to come through witnesses. There isn't any other way.
The real shame would be if the judge let the trial proceed in secret because of national security or some bullshit.