Open Music History
It would be real nice if Musescore would reopen tunes that you had open when you shut it down. Every time I reopen Musescore I have to reopen the music I'm working on one sheet at a time, a real pain.
I did find a workaround, close Musescore improperly. When it restarts you get a message saying Musescore didn't shutdown properly and asks if you want to re-instate the music that was open. Seems like it would be easy to have Musescore do that when you do shut it down properly.
Comments
In the preferences (menu Edit->Preferences) in the general tab there are options for what you see when you open MuseScore. One option is to restore the last session, which is what you are asking for.