Play the Alamo at Phantom of the Attic May 7th

It depends on how the scenario is structured, how the victory conditions are defined, and what options are available to the Texan player. Obviously much of this is arbitrary, but that's what makes this a game, not a reenactment. For example, there could be a victory point system in place, and the Texans earn points for inflciting casualties, holding out past a certain time, perhaps getting some figures OUT of the Alamo (escapees) successfully, and so on. While the battle results may be a forgone conclusion, given the disparity of historical forces, there is room to define "victory" in different ways.

The main thing is, do all the players have a fun time despite the probably pre-ordained outcome of the game?
If the rules build fun into the game, then it will be a success.