Like the title says, the forsworn (and also a hagraven) respawn after completing MQ203 (a.k.a. Alduin's Wall). Since The Karthspire is supposed to be a "no respawn location", the actors (in the exterior zone) probably shouldn't respawn.
<u>Note</u>: Arthmoor thought that the USKP "may" have fixed this in the past, but I can confirm with USKP 2.0.1 that it isn't (or is no longer) fixed.