I'll be following this to see how it turns out. Maybe you could trim off the corner and somehow repair it??? Or maybe it if is small enough of an area you could trim all 4 corners equally to balance it out?
A fundraiser quilt I made once was on display at an assisted living facility and their dog peed on it but I know dog urine isn't as bad as kitty urine. Before they told me what happened they washed it in hot water (aaaaahhhhh!!) but fortunately it turned out fine. Whew!
Best of luck with this!