A decent approach, as a social platform, would be to use the Reddit model. The content is stripped and replaced with [deleted] if deleted by the user, and [removed] if removed by moderation (with the appropriate log in the modlog). This should maintain the overall comment chain.
I think the issue may be federating the update to other instances. I'm not sure how it works now, but if it's treated as an edit, that should work like they currently do.
I'm GenX, and I wouldn't answer a poll if you paid me. I will vote, and I will never vote for a Republican for the rest of my life. If there's no Dem candidate on the ballot for a specific office, I leave it blank so they can see how many votes they're not getting when they don't run a candidate.