Rotors are pretty much just chunks of plastic that should last a long time as long as you don't bang them into stuff. There are varying degrees of damage that can occur to them that will leave them functional, albeit not optimally. If you get cupping on the tips or along the trailing edge, you can probably still fly but your battery life will suffer. We have even flown with sizable chunks of tips missing. Did it work? Yes. Did it lead to more serious crashing and damage? You bet!
Take care of your props. They are all that is keeping you in the air.