He won't last long.
Usually, people might say that someone "wont last long" to mean that they can tell a new situation for someone will not go well and they'll quit, e.g., in this case, when a new employee at a company won't fit in. But here, the new employee is made of bubbles, which literally do not last long because they pop, so the joke is that he physically won't last long (instead of socially).