* He became a zombie: This is the most likely scenario, considering the widespread zombie outbreak in the universe. It's possible he was infected and turned, but there's no explicit confirmation of this.
* He died before the outbreak: He could have perished in a battle or incident before the zombie virus spread, leaving him unaffected. However, this seems less likely given the sheer scale of the zombie apocalypse.
* He survived: It's possible, though less likely, that Nightcrawler managed to find a way to survive the zombie onslaught and remain uninfected. This could involve hiding or escaping the infected areas, or potentially even possessing a unique immunity.
The issue:
The Marvel Zombies comics don't provide a definite answer about Nightcrawler's fate. We see him in a flashback sequence where he appears to be a zombie, but this is not definitively confirmed. He's also not shown to be a zombie in the main storyline.
In conclusion:
While there's no solid answer, it's most likely that Nightcrawler succumbed to the zombie virus and became one of the undead. However, the ambiguity leaves room for speculation and alternate interpretations.