I would let them play the character and they'll end up dying normally. Hell, they may be one of those rare "I survived with a junk build" type of people. Heavens know I've ran with many of them.

Don't try to focus fire on him though, as that's going to be a bad time for you. People remember that stuff later down the line. And it's just better to present the disadvantages to their choices, in challenges as they appear.