What kind of music does She like? In addition, is there some type of music She doesn't like all that much?
Is it possible to kill him through any means besides destroying his metal heart? Also, what would he do if his body became irreparably damaged?
Technically if you somehow manage to destroy his soul that will also do the trick, but soul destroying isn't actually something that you come by very often: it's possible to take a soul out of a body and even place it to another vessel, but breaking it is a whole other thing altogether. The easiest way to kill Colin is to just smash his heart as that's the equivalent of killing a mortal.
I think he would probably either destroy his own heart or ask someone else to do it, although it really is a last chance sort of thing. I'd imagine he would probably try to come up with a way to come by ie. being depended on someone to carry whatever remains of him, but really I'd imagine Colin would be willing to part with life when he no longer can survive on his own. He knows he has already lived a long life and as someone who deals with souls he really knows mortal souls are not meant to live forever, so he'd leave this world in peace.