My windscreen holes were polka-dotted, not striped...
Take bolt you have and match it with another, longer bolt of same diameter and thread pitch. Metric bike, so I am guessing a 5mm x .8 or 6mm x 1 bolt. You can rob something off your bicycle or go buy one at Home Depot, etc.
I'd bet nothing is stripped/striped/dotted, but that the "nut" fell back in a bit and is just not close enough to end of the bolt you are poking at it. Two options
1) If longer bolt works, leave it.
2) If longer bolt works, but doesn't match, splooge some shoe-goo or silicone or sticky booger in there when nut gets pulled "up" with longer bolt. Now remove bolt without pushing nut in and re-install proper, shorter bolt.
What'cha doin with a windscreen on a 919 anyway?