Inara. Making men (and women) sweaty since 2002.

Well, it's an AU. If the Independents didn't lose, Mal might be older and wiser, but not really have so much reason to be bitter.

Unless Shadow got blown up again I guess.

Three major character-forming moments for Mal:
Serenity Valley
The Destruction of Shadow
Inara leaving him/dying

Take away any of these and Mal is a different man, follows a different path. Since the third may or may not happen (unresolved in canon), the path that Mal follows is open to interpretation. But I see these three things as the watershed moments for the character of Mal.

Hmm, let's see. The destruction of Shadow was likely either the start of Mal's sense of loss, carefully concealed or used as fuel for Mal's righteous crusade against evil-doers, or was an additional blow after the Serenity Valley.

Serenity Valley convinced Mal that there is no justice in the universe, and that God had abandoned him.

The loss of Inara would convince Mal that it's better not to get close to anyone (or allow them close to him) because people just die. He cuts himself off from the world and lives his last years alone, thinking occasionally about the future he might have had, then destroying whatever reminded him.