What happens when everyone on a team disconnects or leaves in League of Legends?

I was playing League of Legend earlier today and someone disconnects from the game. We were actually in the lead before he disconnected but because it turned into a 4v5, we started to lose.

Due to this fact, someone decides he was done playing and rage quits. And of course the other two did the same as a 3v5 was definitely hopeless. I decided to stay just for fun so it turned into a 1v5. A one man army.

I was curious what would happen if I was to leave too. Would the game end as though we had surrendered? Or would the game keep going for a certain amount of time just in case someone reconnects. This is especially relevant in cases where you are having a LAN party and the internet goes out momentarily.

What about if you are having a LAN party with 10 friends and are in a custom game together. If the internet goes out, what happens to the game? Will it automatically end or will it continue for a while in case the players reconnect.

What happens if a full team leaves the game

The game keeps going, 0v5.

The opposing team will just have to destroy your nexus to end the game.

You can see this in the following pro match, where one of the teams decided to surrend before the 20 minutes mark, having had a really bad early game :

What happens if all players in the game leave

This one may be a bit trickier to answer, as there is no mean to trace the game once all player left.

Based on the behavior if a full team leaves, I guess the game would still continue, until one of the team has his minions destroying the ennemy nexus (which will happen at one point, try it in a custom game).

As suggested by Lyrion, it seems that if all 10 players are disconnected from a game (or leave the game on purpose), they will not be able to reconnect. This could imply that the game has been ended. However, this observation was made in a custom game, and this behavior may be specific for these games.

I encountered exactly this scenario recently.

Four friends and I were playing a game as a premade 5. Shortly into the game we noticed that there were no enemy champions. We began wondering where they were. At 5 minutes into the game, we received the enemy has disconnected message for all of them.

The game continued; we just destroyed their towers and eventually their nexus. The game lasted only 9.5 minutes and was quite boring. In essence, you don't want this to happen to you, as it becomes a very boring game. In fact, it's a 0v5, and you continue playing until you win.