his eye will never lose its light since it was transplanted
then he becomes a fodder xd
His eye is trasnplanted,we don't know if he'll loose or not his light.Until now all effect of using mangekyou are affecteing his body and his chakra,ther is no trouble of vision.
LOL I wanted to say this exactly XD
I wondered this myself. but kishimoto wont let kakashi lose his sharingan unless hes gonna kill kakashi off. his sharingan is what makes kakashi the copy ninja. its a big part of his character. kishimoto would kill kakashi before changing his character imo