He was supposed to die in combat beneath the freeway after backing-up Bonecrusher in his fight with Optimus. If I'm remembering correctly, Optimus smashed him against one of the freeway pillars. And the reason that didn't happen was they basically ran out of time and money and decided it was relatively unimportant compared to all the other stuff they had to finish. Plus, I believe it was Bay himself who decided Barricade was just an awesome character whom he was ultimately glad got overlooked at the end of the first film so they could further exploit his potential in successive films. Presumably, he was just lost in the shuffle and chaos of the writer's strike of '09 and the rush to get things moving on Transformers: Revenge of the Fallen. And if he was originally scripted in the role of Sideways at the start of that film, I've always wondered if maybe he wasn't replaced for a more lucrative deal plugging a different alt. mode.