Indeed - When using User Scripts you can just run the script in the background
I was actually able to recreate the "Transport endpoint is not connected" - But i can only recreate it when i close down the mount script incorrectly for example in your case closing screen before unmounting. Also i could fix it by unmounting correctly and then remounting, without restarting.
This also made me discover that i can still browse the mount from my dockers even when it's unmounted and cant be browsed from neither cmd line or my samba share. I can even playback media. It seems the mount somehow survives inside the dockers even when unmounted from the system.