@shindig: If there is more money to be made, and neither guy is totally shot, they will keep fighting. There are still good opponents for either, win or lose. If Floyd wins, he could fight Amir Khan or move up in weight to fight Miguel Cotto for the Middleweight title in a rematch. If Manny loses, he could fight Juan Manuel Marquez for a fifth time or fight Terence Crawford. If Floyd loses, there will be a rematch, almost certainly guaranteed. Floyd's pride could not take such a hit.
@shindig: I doubt that very much at all. Why would either retire when they are still in good shape and the two best boxers in the sport? If Floyd loses, or if the match ends in controversy, there will definitely be another fight that will be an even bigger event.
@animasta: It is a soap opera like story. Back when the fight was first contemplated in 2009/2010, the Mayweather and Pacquaio camps agreed to everything (money split, venue, types of gloves to be used, order of ring appearance, cable network, etc.) except for drug testing. Floyd wanted a more stringent drug testing program than what Pacquaio wanted, and so the fight didn't happen. A few years later, there was another round of negotiations, but Mayweather would only offer Pacquaio a flat fee of $50 M USD for the fight, an offer considered insulting by most boxing observers who felt as a marquee name Pacquaio was entitled to more. Only in the past four or five months had there been serious discussion about the Fight happening, since both boxers are out of big-name opponents and boxing fans are sick of waiting for them to fight each other (both fighter's PPV numbers have gone much lower in recent years). That is the basic story.
I think there is every reason to believe that the Fight will be exciting and competitive. While he is not the hyper-agressive destroyer he was five years ago, Pacquiao still comes forward and throws lots of hard, fast punches from awkward angles. Floyd will not be able to sit back and counter-punch at his leisure, like he has in so many of his fights. Manny is also a southpaw, something that Floyd has not seen in a long time. Floyd will have to be much more aggressive than he normally is. Unlike many of Floyd's previous opponents, Manny will not give up if he does not have early success. While Floyd is an early favorite in the sports book, journalists do not have a clear favorite as to who will win.
While boxing is nowhere near as popular as it once was in the US, it is not dead, and is definitely not close to dying. In fact, there will be more boxing on US TV (including free, over-the-air network TV) this year than ever before, as Al Haymon tries to take over the sport with his "Premier Boxing Champions" TV series.
While both fighters are older (Mayweather turns 38 next week, while Pacquiao is 36), and perhaps not at their absolute prime like they might have been in 2010, both are still widely considered to be the two best Pound-for-Pound fighters in the sport by crediblejournalists, and remain the most popular and identifiable boxers in the world. That is what makes the fight still so interesting. Also, the HD PPV is expected to cost $100 USD...