i usually find a "point of no return" when there is an entire team fight, when half your team dies, and their team all lives.
gold from assists is ridiculous at this point.
for example: 4v4, 4 people kill 1 other demigod.
thats 1000 gold + [3 * assist gold(i think its around 200 - 400 not sure)] for the whole team just for a single kill..
also factor in:
-the experience for killing for each demigod involved/nearby
-30 seconds of your team out numbering the other team 4 to 3(possibly longer if they dont/cant tp back right into the action)
-30 second increase of the chance for more kills
-30 second increase of the chance for flag capping
anyway, thats the reason i find comebacks that much more difficult.