Worst Case Scenario: Dante goes Devil Trigger. If I recall Zero's "Untapped Potential" or his awakened form can only be activated if the Zero Virus fills his systems completely. Also like I said about Dante earlier. He got impaled in the heart by his own sword (almost the whole sword went through his body) and got up as though nothing happened. In Devil Trigger his speed and strength is increased. Though you have to take into account that Dante never takes his fights seriously, while Zero does.
Do you really think I'm that stupid? *Walks into a door* Okay maybe I am that stupid...
You also have to take into account that Zero even at the brink of death he will still try and continue to fight, and Zero is one of the most skilled characters in the X series if not the most skilled. Only able to fight X on even terms.
No, worst case scenario: Auditor comes in and beats both of their asses.
Sometimes when you're driving down a road, a bug hits your windshield. It's ugly and unpleasant, but you just activate the wipers / cleaning fluid and it's gone in a few seconds. It's just part of driving down the road. You don't dwell on it, because that'd be silly. Bugs aren't worth the time.