It would depend entirely on your POD. Unfortunately, I have to go against you there and say the most likely scenario is Pompey winning Pharsalus. As has been pointed out, he had plenty of opportunities to make a grab for sole power, but didn't even think about taking them -- Gnaeus Pompeius wanted to be first among equals, and that's hard when you round up your equals and have their heads chopped off in the Forum.
So let's say Pompey ignores all the puffed up aristos in his command tent, imposes his will, and sticks with his (probable) plan to attrit Caesar to death in Greece. He then returns to Rome in triumph. The Optimates are not going to sit quietly and hand a dictatorship to Pompey with a smile, nor will they even tolerate the idea of him becoming First Man in Rome. They would turn on him and try to get rid of Pompey too, and I doubt Pompey would sit still for it. Pompey has the army, and most of those aristos were proven idiots, so Pompey fights a brief, short civil war, and then has to proscribe to pay all his veterans off, so the surviving Ceasarians and Optimates wind up on the chopping block.
Not wanting to be sole ruler in the first place, Pompey follows Sulla's model of using the dictatorship to set the Republic back up, but on a conservative footing and based squarely on his own followers. He relinquishes the dictatorship, but instead of retiring to Picenum, he assumes his place on the front bench of the Senate. However, Pompey is ill-suited to lead by influence rather than command, eventually becomes obnoxious to his faction, and winds up assassinated.