is there anyway to sculpt on top of something that has already been uv mapped without losing and having to redo the map? I imported image as plane, and so it started mapped and thus is probably not a complicated map, idk. But then I added the material images and disp. map and all the vertices and tweaked this to get it looking right.
Now I realize I want to add some more detail in sculpt mode. And if I do lose the uv map info, get’s stretched etc, is there a simple way to get it back or will i have to start that part over?
Sculpting will not affect the the UVs unless you use dyntopo, in which case you will lose the UV information. Normally I use dyntopo sculpting to create something that will be normal baked down onto a lower resolution mesh in which case only the lower resolution mesh needs UVs (sometimes I use the shrinkmap modifier and some manual tweaking if I made significant changes in the sculpt). In your case I think your best bet is to make a copy of the mesh and try and transfer the UVs to your sculpt after you finish sculpting. I think there is a tool that does this in the magic UVs addon.
If there’s no change in topology (adding or deleting vertices) then you’re good, no need for a new unwrap. If there are changes in topology, you can still transfer your old UVs onto the new geometry with the data transfer modifier. Make sure you keep a copy of the old object on another layer.
Just to add to the above, if you need to increase the density for sculpting without dyntopo, you can always subdivide the mesh in edit mode, either globally or locally, or add a subsurf modifier and apply it; in any case the UV map will subdivide accordingly.