I don't think he'll get blind. According to Madara & Itachi, Mangekyo Sharingan's blindness can be denied/reversed via transplantation. Kakashi got his eye via transplantin in the first place. So, I think blindness won't be applied in his case, but what applies to him is heavy chakra drain. We all know that this chakra drain caused his death during Pain's invasion, and thats even after him not overusing it like Sasuke did.
This is just a speculation, so could be wrong. But this is what I think. (Besides, he's not a stupid and doesn't overuse it.)