I have to wake up for work and would have no time to do this tomorrow so I will try to put this together very quickly. Anderson Silva vs. Nick Diaz would be one of the worst mismatches at high level MMA ever. Anderson would completely demolish Diaz in my opinion. I can give one example to base my whole argument on and that would be enough but ill list a few. My first is the Carlos Condit fight. Condit is an extremely skilled and dangerous fighter and very good striker. That being said, nobody would be delusional enough to think Condit is near the level Anderson is. If Condit was able to beat Diaz standing en route to a decision, Anderson would either play with his food or just plain demolish Diaz by the end of the second round. Diaz relies on his high output 70% power boxing that is also reliant on him having a reach advantage as well as his incredible cardio. Against Anderson, a far superior fighter and more specifically a striker, he would not be able to employ his usual gameplan of cornering his opponent and smothering them before unleashing his endless barrage of strikes. Silva would simply bob, weave, and use superior foot and head movement to dance away from the very flat-footed approach of Diaz while sniping away until either dropping and finishing him or taking a decision. You might think Diaz can pressure Andy but look at any of the fights against pressuring strikers he has fought: Leben (ouch) Griffin (Ummm) Marquart (awesome finish).
Now maybe that Cesar Gracie Blackbelt might come in handy but lets be realistic. Silva is a very legitimate BJJ blackbelt in his own right and I seriously doubt Nick would have him in much trouble if the fight hit the ground. I also seriously doubt the fight CAN hit the ground anyway. Diaz has underrated wrestling skills for sure but he is not Chael Sonnen or Dan Henderson. He cannot blast doubles or suplex Silva so I do not see how he would be able to get it to the ground even if he wanted to.
Bottom line is that Diaz although an incredible fighter is in no way, shape, or form able to pose any real challenge to Silva and would really end up making either a nice highlight reel KO or just get pissed off as Silva toys with him.