Grounding Fire (almost) - Now What?

Well first off I'm happy your car didn't burn down. Usually an alternator wire burning up cause the whole car to burn down more than half the time.

You can patch in new section of wire if you choose. However a wire burnt up like this mean the heat from that burn up ran up and down the length of that wire. depending on how hot it got the copper could be crystallized along the wire and making the whole connection questionable.

I would say yes you can patch it. but if your wiring is still the stock wiring it might be time to replace that part of the harness. Or even do a custom wiring job.

just my 2 cents