A teenage or college-aged atheist shouldn't announce his apostasy until he can finish college with a marketable degree, get a job, pay off all debts down to zero and then save up about a year's worth of living expenses in case he becomes unemployed.

(Relevant to your general idea, tough not to this particular case:) Unless he knows his parents are open-minded enough.

The fraction of theists in places such as western Europe has been plummeting in the past decades, meaning that there have been lots of atheists with theist parents, and I don't think the fraction of those who deconverted (or announced their deconversion) before achieving financial independence is that tiny, and yet there hasn't been any societal crisis due to that. Which means that there are plenty of theist parents who don't burn their bridges with their children upon discovering they're atheists. (Same applies with s/theist/heterosexual/ and s/atheist/homosexual/, too.)