Can I salvage this broken toilet flange that's embedded in concrete?
They make toilet flange repair rings. I don't have any personal experience, so I can't say how durable they are, but for a couple bucks it's worth a try. You can see that there are holes to screw through the plastic flange holes, so in your case I'd get a good concrete bit and some tapcon screws.



sample image from homedepot.com, no affiliation