That method works for for a non-combat situation, I suppose. I think letting the roll slide for multiple rounds gives a huge pass to the combat magus with Magic Addiction. Probably a better method is to roll for addiction at the end of combat based on the highest spell cast, and no bonus for any spells cast in between. This can streamline combat, but still maintain the essence that the character afflicted with this Flaw can't just stop at the end of combat. He still has to deal with the highest level spell cast.
I would think in combat (where you are less likely to cast a lower level spell in order to enjoy following it up with a more powerfull spell) is exactly when the "unstreamlined" rules should be followed to the letter, if your mage doesn't want to resist the addiction (combat is also the biggest justification possible for overuse of magic) then they don't have to roll that round, but if they want to start toning it down to give them a chance to negotiate, or avoid unconsciousness, then they need to start making the rolls.
A player would almost always want to roll, just so they have control - their character can keep casting if they want. However, as a SG, I'd have to respect any player who RP's the addiction and declines to even try to gain control before they need to (and would possibly cut them some slack in some other way - a better story needs to be rewarded).