Stratego. Both opponents have 40 units each at the start of the game. My question is, is it real to destroy/kill/capture all forty enemy units during a single game? By "destroy" I mean also passive or mutual destruction, not necessarily an active kill. For example, if the opponent's spy is attacking our general, it is still counted as we have killed him.
As Dennis_E mentioned, it is possible, but I would say it is improbable.
To destroy all enemy units, you would have to avoid the flag until the 40th capture. Additionally, one of the enemy's non-stationary pieces must be the 39th piece to be captured, and it must suicide itself on one of your pieces. Otherwise, the game would have ended beforehand as the opponent would have been unable to move any piece during their turn, thus losing before you could destroy all 40 pieces.
What makes this improbable is that without assistance from your opponent, you would have to identify all the non-flag stationary pieces and destroy them before destroying the flag while ensuring the opponent maintains an additional non-stationary piece, which they must voluntarily throw at a piece that would destroy it on a turn preceding one where you are able to capture the flag.
I really cannot see a human opponent not forfeiting at this point unless they were colluding with you.
I question the "improbable" about this. We've had lots of games where all the miners were eliminated, leaving it to the blood kill. (Yes, we know the importance of keeping a miner for the end--dummy flags are dangerous weapons.) If the weaker side has no scouts left this goes down fairly rapidly. If he does, we've seen drawn games due to the minimum number of pieces required to catch a scout (seven on the open board).
Possible? Of course.
Realistic? That depends on your opponent's level.
Computers for example are really bad at Stratego. Against a computer, you can win almost every time by capturing all pieces. Against a decent human player, you should focus on capturing the flag ASAP.
But if you are so far ahead that you are in a position to utterly destroy your opponent, your opponent can just concede the game before you get the chance, especially when playing in a tournament setting.
I don't think it happens very often.