Polyester will last a good long time. It would be far better to reuse it once it can no longer function as a bag. You could shred it and add it to your compost heap or topsoil as a soil amendment, or you could cut the bags to flat and use them as a kind of landscape fabric or for anything else for which you think it would be useful.

I ended up returning my polyester bags for cotton ones. I like them just as well and I know they will return to soil. I will just buy some more when they wear out.