I agree that if an army is marching to fight and the city teleports, then the army should not fight whatever random level npc force replaces the city.

I have also seen server resets drastically change the force in a valley while an army was marching to it: also not good.

as for whether teleporting will be a major factor in warfare, I think it will happen, but will be minimal (but still, annoying). If somebody actually wants to spend a bunch of coin on scrolls and just keep running away, oh well...plenty of other people to attack. besides, it will make winning one on the wheel more useful, like a having a "get out of war free" card.