Just about the only way its a done deal is because you can stick a fork in it... turns out Pride was just dicking around UFC, and then UFC jumped the gun with the announcement. Pride pulled out of the deal, and it wasn't going to happen. However, from what I heard, after Silva got his head kicked in, Pride tried to bring it back, but UFC said they didnt want a loser coming over to fight.

So right now, its very improbable to happen, but theres still a chance.