my cat wouldn't take a collar. we kept putting them on her, but she would lose them after a day, so we stopped trying. she was an outside cat, and one day she came up missing. turns out the neighbors had found her and taken in as a stray.
first thing they did was have her fixed. the problem was i had already done that about 14 years ago. but the vet didn't seem to mind taking the money anyway, so she got fixed again. she came back limping after a week or so, and then we finally found out what happened about a month later. this was about a year ago.
she died a couple weeks ago, buried her in a corner of the yard. 16 years old i believe, so it wasn't premature.