Use these steps to export your Unity scene and import into Maya. Render your Unity scene in Maya..
Select Window->Package Manager
Choose Advanced->Show preview packages
Select FBX Exporter
If FBX Exporter does not show up, reselect the options pictured a few times.
Close the window
Select the models you would like to export in the Hierarchy, (Primitives will export too.)
You may need to open the parent and select the child models.
Choose Game Object->Export to FBX...
Export into your Assets, you can move the file later
Choose File Import...
Import the fbx file into Maya
The file might be scaled extra large
Select all the objects, use the arrow up key a couple times to select the parents.
Select Edit->Group (This will put everything in the scene under 1 node.)
Use Windows->General Editors->Hypergraph: Hierarchy
Alt Key, Left and Middle mouse to zoom out
Scale the top group to .03333333 in X, Y, Z
Move the model so the ground is at 0,0,0
Move all the grouped parts out of the hierarchy
Carefully select all the objects below the top group
Use the Middle mouse key and drag all the objects out of the hierarchy, in the hypergraph
Make sure your texture files are in the same folder as your Maya file. That way Maya can find them quickly.
Refer to Texture map page to help you decide how to manage textures, especially Transparency maps and Bump maps.