I assume you are refering to floor tiles you 'painted' in with WF map edit.
Well, there are ways around loosing them, but this really depends on what changes you are makig on the map, and the area you are changing.
If you are just changing a small area, you can use UO Copy, and copy the new map area you modified, hopfully around your floor areas.
But if your floors are within the area you are modifying with the bmp, and dragon.. you could simply copy over the new map area in whole.. then, go back and copy in (using UO Copy, or UO Map Copy) your floor areas you had, individually, into the new modified map area.
that make any sence?
Ay way you look at it, if you have to edit the map with Dragon, after you do a lot of World Forge work, you are going to spend a lot of time piecing parts back together.
