<Snipped quote by harinezumikouken>
I don't think that's necessary. Mana comes back slowly enough that it can be treated as a finite resource in an engagement. If someone runs out of mana, it'll be some time (half an hour or more depending on the person) before even a single spell can be used. Plus, mana consumption makes the user tired in the same way as physical exercise.
Alrighty-rooty.