I think his back injury should have been retirement tbf so it's not a bad comparison. Not 100% certain too but I think Austin has said he could go for the right last match, just the opportunity hasn't came up. And at this point it probably won't
I agree Sting should have been retired, Id hate for him to end up crippled because he couldn't resist that one last match, ditto with Austin. They both having nothing to prove so shouldn't risk it, but hey it their choice if they do just hope it works out for them and they retire safe and in good (or as good as a wrestler can) health wise.
From Tony Khans tweets it sounds like this isn't someone coming in for one last match but a more frequent amount of match's but i could just be reading into it how i want it to be.