Gambits are not essential for survival at all. Up until I got tired of casting Poisona, Blinda, Esuna etc the most I used on any one Character was three slots my lowest amount of Gambits being one on a character.

Though they are not essential, they are useful. Even using the "Wait" battle system and entering all your actions manually doesn't come out on top in terms of time efficiency compared to "Active" battle system with Gambits.

I wouldn't worry about saving "precious licence points" though, since they are so easy to get. I often have more than 500 stacked on each character, I don't have much to do with them anymore. If you want to get some really fast LP without grossly overleveling your characters equip that thing that Doubles LP gained (If you have access to it - if not this is still effective) and blast through lower level enemies.