I would let the initiative continue, the chance of succes is vey big but still there needs to be an risk..
The players need to understand that death is an bad thing and dont think to easy about it..
Otherwise you will get this:
Player1: I fall unconscious, bleeding heavily
Player2: Ohhh we are almost done, we just have to finish the fight in a few rounds..
*3 rounds later*
Player2: Dang it, why wont the monster fall..
Player3: You had 2 bad rolls didnt you? Ill come..
DM: You move closer but cannot reach him
Player1: Rolls, an 8.. You hear me gurgeling for breath and then i lie down motionless..
Player 2 and 3: Dang it, we thought we could kill this creature sooner, sorry man..