Put two smart fighters in an open field with no judges and the one who has the best combination of quick feet , takedown defense, and endurance wins. It could take several hours, but that's what it would come down to. Don't let your opponent get a hand on you, strip their grip if they do get close, run away, come back only when your opponent is tired. Pretty boring, but mobile armies have used this tactic for millennia with their skirmishers. You're going to have to put some sort of boundaries if you want a traditional fight (ie two guys facing off against each other). Every form of sport combat has boundaries for that reason - without them one person keeps escaping and coming back until his opponent is tired.
And even within a bounded field (say they fight on a football field instead of an open field), the problem with BJJ is its lack of takedowns. Being great on the ground is meaningless if you can't get the takedown; you currently have to mix BJJ with wrestling or judo for that.
BJJ spends 90% of its time on the ground, which is why it is so good on the ground. But if you're spending 90% of your time on the ground and 10% of your time on techniques to get the fight to the ground, you're simply not getting someone who spends 90% of his time standing grappling to the ground. The only reason things like guard pull work is because under current BJJ rules its illegal to stall by refusing to follow to the ground. Guard pulls are trivially easy to stop if you're allowed to stall; that's why judo and wrestling developed so many other kinds of takedowns.
As for Royce beating Hughes without time time limits and boundaries - did you watch the fight? He was finished on the ground. A better argument would be that Hughes studied BJJ and used it along with wrestling to beat Royce. Time limits are a non-issue when you're finished.