Originally posted by Eightball:

The content drop that added the Mistlands also changed the land building algorithm a bit so to create larger Mistland land masses.

So you will be able to find the Mistlands in your current world, but they may be more a series of broken, small islands than the larger land masses you would get starting a world post content drop.

do i lose anything important? like no boss spawns and whatever?

Originally posted by Eightball:

And don't forget, with just a small effort you could transfer all your high value items to a new world with your character if you so choose, so your past effort would not be lost.

well.. it's less to do with my items and more to do with this massive base i've spent atleast 70 hours on.