Fair enough, usually the answer is “very” but it’s not like complete purges of ruling lines happen that often.
Complete purges are rare. Usually usurpers will marry into it to legitimize rule. And even when they don’t it’s usually the worst (moral) middle class/lesser nobility/military leaders to take the reins. To our knowledge one servile war has succeeded and doing so has left a nation impoverished to this day.
Kind of weird to call out Haiti specifically in this situation, especially considering all the ratfucking they went through at the behest of the imperial powers.