No. it is not possible since the original GameObjects, which the collides are attached to, are removed.
You could technically use any mesh combine tool with this. Maybe there is something on the store which fits your needs better? If you want to return to editing the map you would just use the "recreate map" option under Map Tools. When the map is "recreated" the objects under the map object is destroyed and the tile objects added back. So if the mesh combine tool placed the combined mesh somewhere else you just need to manually delete that.
If you have Poly World check its tools. I think it might have a combine tool capable of preserving the colliders. I am not sure though so first ask the author if you do not already own it.
Another option is to just recreate the colliders with cubes where you remove the mesh renderer. This will allow you to make nice simplified collision areas rather than having a bunch of separate colliders next to each other.