As I have stated elsewhere, Mueller was putting the screws to Manafort, Flynn, Papadopoluis, Cohen, etc. to try to get them to "flip" on Trump and confess to colluding with the Russians. Since there was no collusion, there was no way to "Flip".
Once Barr is done with his probe into the "why" of the FBI and CIA beginnings of the probe, I predict pardons all around...