When and how did Antonio bite it? Because if he never lived at all, Mexico would be unrecognizable by the time of the Mexican-American War. In the later days of the Revolution, he was the leader and champion of the faction that wanted a notionally republican state that was also racist, militarist, and somewhat deferential to the Church. To my mind he had few or no understudies - if he goes down that early, his whole vision goes down with him, and it's a struggle between de Iturbide's constitutional monarchists with extreme deference to Church, and Vicente Guerrero's secular democracy with racial equality. Guerrero will lose because supporting him is against the self-interest of everyone but the Indian campesino. With that, who can say if or how Texas happens?
If Santa Anna had died later, say around 1843, then it depends on who succeeds him, but I have to say his generals were of much the same cloth as him by that point - he'd promoted men who thought like him, which meant self-absorbed gloryhounds who held their men's lives cheap. I don't know who would have done better by that point.
Kill him in 1830 and I have few ideas about what you'd have a decade later.
So when and how are you offing the fellow?