Here is something I was thinking when I read your post:
Landscapes such as the one you first created can suffer from any degree of irregular geometry. The intricacy of such a landscape could become a real retopological nightmare
I just tried something in Blender, and it seemed to work quite well for landscapes that do not contain extreme vertical irregularities (assuming now you have your landscape mesh file open):
If you create a relatively high-poly manually-subdivided plane (i.e. enter Edit mode, select all vertices in plane, then subdivide several times), then scale and place the plane so that it hovers just over and covers your landscape mesh, you can then try the following:
Make the plane a Cloth by going to the Object Panel (F7 key) then selecting Physics. Under the Cloth tab, click the Cloth button.
Next, select your landscape mesh and set it up to detect Collision by clicking (under the Collision tab) the Collision button and setting Damping to 1.0.
Press ALT A to let the Cloth simulation begin to calculate.
Notice the frame at which the cloth seems to best cover your landscape and press the ESC key.
Manually move up to that frame using the Cursor Right key.
Select your subdivided plane.
Back in the Editing window (F9 key) go to the Modifier section. You should see a Cloth modifier listed. Click Apply.
If the end result turns out well, you can now use this mesh containing only quads in lieu of your original mesh
For better results / more details, you might want to manually subdivide the plane one or more times as well as increase (slightly) the Quality level of the Cloth setting for the plane in the Cloth panel.
With higher subdivision and quality, a cloth simulation can take a while to process, but the end result could be worth it.
The newly created mesh could be substantially better for texturing as well as sculpting additional details in Blender.
Best of luck with your project!