The game client tries to reconnect when it disconnects. Your units stop, the game freezes, and you get a status update on the left. Depending on what is happening, you can end up losing the game anyway even with a reconnect. On a reconnect, your client moves in turbo mode until everything is caught up.
Oh yeah of course there's that, you still get permanently disconnected if you don't reestablish connection within a short space of time. If your connection issue requires you to restart your router, you're boned.
I thought you were talking about a feature that enables players to rejoin a match in progress after they've been booted from it, that would be useful in team games.