Out of about the 20 times that I chose the 'Not Now' option on the many Evil (Dremer) portal quests I got, I got a bugged result only the one time. The rest of the times, the result postponed the quest properly.
This one time, it reduced my mana by 100 and announced that the bridge was now open (which was one of the options I had not selected). Afterwards, the portal was not in fact open however. See screenshots. As you can see, in the second screenshot which was taken after the quest screen, the portal above the city is not active.

This one time, it reduced my mana by 100 and announced that the bridge was now open (which was one of the options I had not selected). Afterwards, the portal was not in fact open however. See screenshots. As you can see, in the second screenshot which was taken after the quest screen, the portal above the city is not active.

