If the vent valve breaks off, then what?

I am dong the axle vent mod. The valve has been soaking in WD 40 for a few days in anticipation of removing it. Well, today I tried to remove it and it wouldn't budge and then the bolt started to round off. I can remove it for sure if I wanted to (vise grips), but what if it breaks which looks like where this is heading? I've already blown a pinion seal so I really want to do this but not at the cost of a broken valve. Has anyone snapped it off and what did you do?