This.

I don't know that much about the travel insurance - may need to call the provider or have a look at T&Cs very carefully. However, from a UA perspective, the ticket is re-issued. There really is no such thing as a cancelation on a UA ticket unless its a fully refundable fare (with or without a fee). Really, any cancelation on a non-refundable fare is just a change and re-issue. It can be immediate (ie, you change to new flights right away), or you can cancel the segments on the itinerary, and the PNR remains intact with the funds attached, and then re-issue new tickets with your chosen new itinerary using those funds (plus any additional add/collect) for whatever new flights you book. Either way, it's essentially a change.

To look at from another angle, you are not eligible for the flexible 24 hour rebooking policy (/cancel) when you change a flight (that's UA policy, which I haven't been keeping up with very lately, but which has always been more flexible than what the DOT requires). I suspect any travel insurance will see it the same way.