[TheCrimsomBlade]

it all depends or what kind of resistance the creature you use the spell on has.
some creatures are not effected by charm spells and it also depends what level your druid is compaired to the creature he's trying to charm and then again every spell has a chance to fail depending on the save roll the creature your trying the spell on. Every time you cast a spell at a person or creature that person or creature has a chance to save against the spell its all stems back to the old pen and paper D&D games when we would through dice .
such as an 8th level Druid would through 8-8-sided dice when it attacked and a fighter 8th level would through 8-10-sided dice if the druid thruogh a total of the 8 dice of lets say 8 on each dice then that would equal 64 points then the fighter through 10 dice and all were 9's that would equal 90 the fighter would win that attack with a counter through of 90 minus 64 = 26, that would mean the fighter took no damage at all and had 26 points to spair magic works much the same.
now as far as the spell not wearing off. some charm spells don't wear off as long as you are in the area so if you go back one screen or forward one screen then come back to where the chamed creature is and it should break the spell because charmed creatures cant follow you to a different screen.