A warning really has to come. A healer who vanishes in thin air can mess up everything for a team. Abusers exist, but there are never only abusers on one team. If you have blue = super good and red = terrible, and a loser from blue hears [insert ideal number of seconds (which I think are 15)] before it happens that he will get changed, and he decides to spectate. Blue will still be a bit weaker, though red won't be as strong as they could have. But any new incoming player will have to go to red, and if none comes then the spectating loser will have the choice between playing with a bad team or not playing at all. Probably he prefers the former, and if he doesn't, he won't be playing anymore. He can't go back into blue because there is already someone extra (else there would be no autobalance).