Updated: See note below on how to find your nodes.
Okay, I think the only problem is that, when you reopen your file, by default it displays in "Solid" mode. This doesn't show any textures, and it won't show the result of material-based displacement either, which is how you made your plane into a mountain. That's why you only see two flat planes.
So, after opening your file, click on the "Render" icon:
or alternatively hit "Z" in the viewport and select "Rendered" from the wheel menu.
In addition, your file contains references to the following external texture files. If you still have them in place, then everything should look fine.
/tmp/textures/Seamless mountain rock face texture.jpg
But, by default, external textures like these are not saved as part of the .blend file, and if something wipes
/tmp/textures, you'll lose them all. If that happens, you'll see the plane, mountain, and reflective water shapes, but they'll all be a bright magenta color, like in my screenshot, meaning the texture files are missing.
So, if the files are still there or if you can restore them from where you got them, you may want to save them in the .blend file by selecting
File -> External Data -> Pack All Into .blend from the menu, or check the box under
File -> External Data -> Automatically Pack Into .blend.
You can also move the files somewhere more permanent and then use "File -> External Data -> Find Missing Files" to fix the references in Blender.
In a comment, you also asked about finding your node system. To see the full node system for the ground plane after opening the file:
- In the 3D Viewport, click to select the ground mesh.
- Expand the Shader Editor window on the left a bit.
- In the Shader Editor window, zoom out with the mouse wheel, or use the key sequence A to select all and NumPad Period to view the selection.
It should look like this: