Just had a game where all enemy players left and the game just kept going until the last round because noone joined. A huge waste of time in my opinion.
If all players on the opposite team leaves the game just skips the ongoing round, as OP noted. Game is trying to speedrun to the end.
Then what happens is that the remaining team gets their rounds skipped. And maybe the next one as well. This can manifest as getting 1-2 hero rounds skipped (no points earned)
Then at this point, maybe another enemy team is assembled and tossed in. This team inherits say that 120 points that the first “leaver” team got and then can play the second and at times, third round while the original team has to beat them with only 1 hero round left to play.
It doesnt always happen but its crap when it does : (