In that scenario; I should point out that had it been RC and Xykon against the Sapphire Guard any sooner, Xykon would have known to use more appropriate skills and they would have cleaned most of them up no problem.
Having someone use a spell that has a 50% fail rate significantly hampers their combat potential, after all.
But yes, I agree with the general idea that, given the circumstances, even if Team Evil winning the war was set in stone actually securing the gate was highly unlikely. The "we'll come back in a few weeks and crush the hobgoblins" idea would have been realistically practical with ambushes from thwe Azurites and no trio of high-level spellcasters sitting on top of the throne.