I'd say it'd get at least a million.
This is a fight that hardcores and casuals would be all over, it'd clearly be the biggest fight in the history of the sport so yeah, a million at least.
Don't think it can get 2 million though, I think Brock/Fedor post UFC 100 might have been able to do 2 million though.
THE PERFECT STORM
THE PERFECT RECORD
THE PERFECT FIGHTER