I find many of the things I worry about never happen...and it's easy to over complicate an issue in my head.
Do as you mention in your last comment Mr. Torvy. Cut from the trunk hinge out towards the tree top, using your grapple to protect the fence, or to lift and hold the trunk at the broken hinge point.
5 minutes with a chainsaw cutting a couple of 16 inch sections from the trunk and you're out of jeopardy. The rest is basic clean up.
I cut a tree like this on Tuesday while visiting my son's place outside Tulsa, albeit it was overhanging a pipe fence into his horse paddock rather than a wire fence.