RetroDECK does not delete any save states, they should all be there under retrodeck/states/
There where some bugs in RetroArch we have addressed in 0.9.1b that might have caused the menu option to disappear in RetroArch.
How ever save states are not a safe long term saving method as cores or emulators updates they might break compability with old states.
Always use in-game saves as your default saving method and states as temporary backups.
We hope to one day in the far far future implement ares as well. As we know some people don’t like RetroArch.
But we rather focus on new systems first before adding alternatives.
All we need is more developers xD