Destroying an entire realm is a bad idea these days. You can't fill up the gap and you've just got yourself a lot of angry players who want you gone who will most likely going to join your enemies.
If you let your enemies live as a small realm, they will stay there most likely and will just be weakened. You can sometimes beat that for fun but they can't do anything about so you can entertain yourself and not have a big headache at the same time.
Interesting Fact: With so much ice covering the land, it should lower the sea level and reveal even more regions technically.
