The only person that should ever be in danger of running out of MP is Bard-B. EVER. However, this is where friendship and FC gil pooling come into play. Support your bards by making some contributions to their gil, or toss them some MP restore-type potions. Ergo, Bard-B (bard-battery...bardery) runs low, he/ she just downs a MP restorative-type potion and voila! Everyone stays happy.

Support bards, please! Without us, your enduring fights have the propensity to turn into enduring wipes...and at that point, who cares whose "DPS" is bigger