About Heroes of the Storm: players aren't allowed to leave and if they do, they are threatened to be queued with other leavers. And there's no resign option.
On the other hand, my worst experience with Dota was that a lot of players were leavers, so any sign of losing and someone left the game. And after that it's really game over. No fun to lose the game this way, even no fun to win the game this way. But with HOTS that's completely different. Almost everyone tries to stay until the defeat and it's not that rare to see a comeback and victory.
So I'm supporting that notion of not allowing anyone just to leave. It's not a chess and there are other players who might want to fight until the end. On the other hand, quick anonymous poll, initiated by one player, if anyone wants to stay, and defeat if everyone wants to resign wouldn't hurt anyone, I guess.