Conventional wisdom is that top 80% is safe-ish.

Last few go-around (post 9/11) it was 10-15% furloughs at the majors. Specific numbers will vary by your airline's financial circumstances and in this case route structure since unlike a typical slowdown some destinations are very unpopular or outright banned.

Regionals can vary from growth due to down-shifting of mainline flying, to liquidation.