ToME: the Tales of Maj'Eyal

Arcane Combat's description says:

"... 24% chance per melee attack to deliver a Flame, Lightning or Earthen Missles spell ..."

If you don't have Lightning or Earthen missles, and the 24% chance hits as true - do you automatically get flame, or is there now a 66% chance that the ability does nothing?

Its a 24% chance to deliver an extra magic spell.
You are not penalised for not having spells available.

In fact, you can have arcane combat sustained - but not have learned flame, lightning or earthen missiles. It can still trigger - but as you don't have access to any of the spell checks, you do nothing. :D

If you're starved for points, lightning may also be a better option than fire as it always pierces to the 10 range without requiring a 5 point investment.