You know, Cell's regeneration abilities are wild—he's like a cockroach mixed with a superhero. If he loses his head, it depends on whether his core (that little orb in his torso) stays intact. In 'Dragon Ball Z,' we see him regenerate from just a single cell, so theoretically, if his core survives, he could regrow his head. But if the core's destroyed? Game over. It's kind of like how Namekians work, but cranked up to eleven. Frieza blew him up once, and he still came back, so I'd bet on him surviving unless you obliterate everything.
That said, the real fun is imagining the chaos if Cell just casually walked around headless for a while. Would he still talk through his stomach? Would his voice sound weird? DBZ logic is so over-the-top that nothing would surprise me at this point. Toriyama once had a character survive being turned into chocolate, so a headless Cell feels almost tame by comparison.