I think part of Charizard's personality had to do with what the PokéDex entries say (despite the entry showing up later, I kinda remember reading it elsewhere as a kid): "However, it never turns its fiery breath on any opponent weaker than itself." It could explain why Charizard refused to fight in various battles like against Sparky or even as a Charmeleon against Paras. Meanwhile, Charizard was quick to battle against Magmar, and in the first movie, he turned his flame on Mewtwo almost immediately. And then in Johto, he picks a fight with the bigger Charizard (but a lady Charizard was involved--nudge nudge). It's like Pokémon know when an opponent is strong, it's just some Pokémon have a bit of chivalry when it comes to that. You know?
So while I'm sure part of the reason Charizard was disobedient was because Ash wasn't that skilled of a trainer for a while, I'm sure it's possible he maintained the memories he had as a Charmander, so he stayed. If anything, I think he really was testing Ash to see if he could overcome it and be the trainer he had the potential to be. And by the time he was left in Charicific Valley, he really became loyal to Ash since. If Ash was anything like Damien from the start, I don't think as a Charmander he would've gone along with him, or as a Charizard would've done more to him than just Flamethrowering his face.
And even then, if Charizard had escaped and ran away from Ash, he is bound to the PokéBall. I doubt he would've gone very far, and he would've been discovered to be a runaway trained Pokémon at some point or another.