Co-op: Do you always lose, when teamplayer's structures are destroyed?

I understand, that L&L is impossible, when you are solo, because you need 2 to deactivate those towers.
But on a completly different map I also lost with all of my structures still intact.

I tried to recreate it in the single player arcade version, because i didn’t want to waste other players time… but they are scriped a bit different, and even L&L wont loose the game, even if Im alone.

But whats really interesting: I never had someone destroying his own strctures, just to force a Game-Over. I was probably just lucky.