I can't exactly answer the safety question, but I can say I used a significantly damaged cooktop for a couple years awaiting my remodel. Boil-overs went "somewhere" and I never had a problem. That said, my cracks and missing chunks weren't over the actual burner itself. I'd use the back burners with no hesitation, and try to avoid things like rice, pasta and milk products in the front if you're a klutz like me and tend to let those things boil over.

I'd use the back burners with no hesitation, and try to avoid things like rice, pasta and milk products in the front if you're a klutz like me and tend to let those things boil over.

Well, they could all spill over into the existing oven/cabinet below and I'd never know the difference (at least until we rip out the existing cabinets!)