My smartphone has ability to use two sim card or one sim card plus sdcard. Generally, I'm using second option (sim+sdcard), sdcard as adopted storage. I want to use second sim card temporarily. But if I will unmount sdcard and pull it out will I be able to use it later without problems?
First I moved all apps to internal memory. Then I unmount adopted storage from SD card options.
System starts syncing data that was not written yet and after minute there was intent notification "You can remove sdcard safely". So I removed card. Nothing wrong was happening. Of course, wallpaper disappears but it was predictable.
Another side effect was that I can't save screenshot so I made these photos by another phone.
After some time I inserted same SD card to smartphone and Android mount it automatically. Wallpaper appears again and all my files from SD card was in the same place as before.
Technically adopted storage is separate file system but mounted in a file system, in the specified directory. Not every app can be moveable to adopted storage. It behaves like normal SD card with FAT/exFAT file system but Android merge view of internal memory directory in one "file system". Another difference is that adopted storage is encrypted. Android mounts that encrypted block device, decrypt it and mount in /mnt/expand/. No system data are moved to adopted storage, only apps that developer implement an option to move app data to adopted storage.
Test was made on Android 7.1.1. Smartphone model: Motorola G5S Plus (XT1805)
Q & A