Descent 2nd Edition FAQ v1.2, Familiars wrote:
Q: Can a hero activate a familiar while knocked out?
A: Yes, a familiar can be activated before the knocked out hero performs a stand up action, but not after (because standing up immediately ends the hero’s turn).
Descent 2nd Editon FAQ v1.2, Knocked Out Heroes wrote:
Q: What happens when a hero is defeated during his turn?
A: If a hero is defeated during his own turn, that hero’s turn immediately ends.
If a Necromancer is knocked out during her turn before the Reanimate activates, the turn ends immediately and the Reanimate loses its activation.
If a Necromancer is currently knocked out and the Reanimate is on the board, the Reanimate can activate before she performs a Stand Up action, but not after.