Here is a relevant feature request you may want to support (by pressing the heart button or commenting to explain your use case):
On Linux and other Unixes it is possible to mount an external drive so that it appears to be part of the local filesystem (taking the place of an existing folder). If something like that is possible on Windows, you might be able to add that as a vault (probably twice, once with and once without the drive mounted, so both folders have an .obsidian folder). If that works it will of course add complexity to your setup, may have unwanted side effects in some situations, and you’d probably want to make sure to close the vault before removing the drive.