Nowhere in the books does it says that if you cease to meet the "requirement" then the flaw stops applying. There is no reason to suppose flaws behave like Feats or CW and CM Prestige Classes. So, that's a strictly RAW reading, you only need to meet the requirement when selecting the flaw.

I would also rule that players keep their requirement-gated flaws even if they no longer meet the requirement: they're supposed to be actual character flaws, and the only way they could be "lost" is if the characters overcome them (quite the unlikely occurrence from my experience with flaws), and even then I'd let the characters retain the bonus feats gained through flaws because otherwise it'd be a mess.