A common problem in Clash Royale is either crashing or losing wifi. Something has to be done, so here is my suggestion to fix it.
Once the game detects you are no longer in the game, a message goes to all enemies and your teammate saying a Player has Disconnected, a 30 second timer will then start and if the 30 seconds are up, the enemy wins, but in 2v2 the teammate gets Double Elixir (Quadruple Elixir in Overtime) and your deck.
This will help the game be fair and let you know if your opponent left.
To make it not abusable, it can be done once per game for one player, if they disconnect after that, the opponent is told that you left and they can win the game.