I understand that if you are at 1 and try to use Raven's ability during the recovery, you hit 0 and lose. What if you're at -3, you have Gone But Not Forgotten on the board and 3 stunned guys. Do I get the opportunity to ko a couple guys and move my life back to 1 and then life check is done at very end or is life check done at the start of recovery? and if at start, do I die by going to zero using Raven?

you loose if your have 0 or less live after you recover your charachters (or at the start of the recovery phase) not completly sure, but if your at, lets say -2, and you gain back 3 life before the end phase or whatever, your still in the game.

at the beginning of the recovery phase you check to see if anyone has 0 or less endurance

I dont think you're understanding the question.. In the first sentence of your post, you rephrased my question and stated "I'm not sure."

So can you use raven's ability after the check?

408.2a states that endurance totals are checked immediately after all players pass on an empty chain at the start of the recovery phase.

That means you have the opportunity to play effects before endurance is checked.

The check isn't until the after "the start of the recovery phase" effects resolve and both players pass priority, and the endurance check is PRIOR to the recover (KO'ing) of characters. So yeah, Gone but not Forgotten wouldn't happen in time.