No idea Zell, since I only watch Horrible myself.
This episode was canon, right?
With someone so strong in the guild, the only reason I can think of that he wasn't mentioned in the whole "strongest wizard in Fairy Tail" talk before was that the author didn't think up Gildartz until now. Or it's filler, but that doesn't quite seem like it.
What I also failed to understand was that if the dragon left, why did Gildartz not go back to complete his quest, or wait till he completely healed before doing so if he hasn't already recovered? Again, only one reason makes sense to me - that the damage Gildartz took weakened him forever.
edit: seeing Lisanna again rather re-confirms my idea that none of the female characters alive are anywhere close to forming a romantic relationship with Natsu.