Heard back from engineering on this, and there isn't a guaranteed behavior since it would depend on which event meets the criteria, as well as whether we had already done compaction-time deduplication before the deletion occurs. Since Mixpanel doesn't support upserts, ideally, there shouldn't be non-duplicate duplicates to begin with.
Given that there isn't a guaranteed consistent behavior, I'd recommend fully deleting the event data and, once the deletion is processed, uploading the corrected event data.