It doesn't matter if he wins convincingly or not...if Pacquiao isn't willing to submit to random USADA drug testing, the fight ain't happening...period...so there's nothing to negotiate.
Besides...Bob Arum doesn't want to make the fight anyway. Why put Manny in with Floyd and only get 20% of the pot (because he'll have to split the rest with Golden Boy and everyone else) when he can put Manny in with Margarito, Foreman, or any other Top Rank fighters and get 80% of the pot (because he won't have to split anything with anyone)?
The only way that the fight will happen is if Manny Pacquiao demands the fight from Bob, and if so, then he'll have to take the USADA drug tests. Ol' Arum is going to use that drug testing to dissuade Manny from fighting Mayweather and convince him to fight guys like Margarito, Foreman, Chavez Jr., etc. Is this not obvious to everyone yet?