Pacquaio v Khan isn't confirmed yet but it would potentially be a fascinating fight, and not like the Mayweather, cagey, negative let down. I don't go for all the Mayweather is an all time great argument. If he'd ever really come out of his shell and fought, the way the all time greats did, he would have lost imo.
Pacquaio and Khan come out and fight, and they know each other very well. Imo, the fight hinges on weather Pacquaio is back to his best. Those rotator cuff injuries are excruciating, and if anyone has had one they will know. It would have been a massive handicap for Pacquaio in the Mayweather fight, and much worse than any injury Mayweather claims he also had imo.
The injury will probably have healed, but Pacquaio will need all his speed, accuracy and power to beat Khan who is also very quick with a longer reach. Pacquaio is an expert in breaking his opponents nose, which sounds a bit off I know, but it's a fact, and for Khan that's a big weak point, as it was with Hamed. The only fighter who could still fight well after getting that sort of damage was Froch, who narrowly lost to Kessler in their first fight.
If Pacquaio is back to his fighting best, he will win the fight imo. Khan will try and keep him at range, but he's no Mayweather, and won't be able to do that for long. Manny has a very good defence, and is one of the best at getting inside and hitting with speed and power. One thing about MP, he has never ducked an opponent, and Mayweather ducked MP for a long, long time.
If it is MP's last ever fight, imo he is the best ever fighter (yes better than Duran) in the history of the sport. Also one of the best boxers.