I agree with all on this thread who've stated High Sierra behaves in this manner:
- have three Finder tabs open;
- mouse click Finder's red-circle-X to close it; or press cmd-q to close Finder completely;
- mouse click Finder dock icon;
4a. Finder opens a new window containing three tabs.
I, further, agree with all on this thread who've stated that the behavior of #4, above, is different in Mojave, e.g.:
4b. Finder opens a new window containing only on tab.
I've found a solution that appears, at first blush, to work for me in Mojave.
It comes to us courtesy of the user Eagle on apple.stackexchange.com:
https://apple.stackexchange.com/questions/100433/finder-reopen-last-closed-window/100435
Eagle states:
- Click on top-left Apple icon
- Then click on System Preferences
- Then General
- And then uncheck the box saying, "Close windows when quitting an app"
- It will save your session of Finder and when you restart your system it will show you last opened tabs of the session
This appears to work for me when I perform my original workflow, above, items 1-4a.
Note that it also appears to reopen the tabs to their prior directory/drive locations, if present.
I had not tested that behavior in High Sierra; so I can't speak to that whether it's consistent or not.
Further note that if a tab showed contents of a directory/drive that has been removed/unmounted between Finder sessions.
Finder simply does not open that tab; but opens all other previous tabs that it is able.
I've not tested how this System Preferences->General change effects, or afflicts, other applications from session to session.
So, as you'd surmise...YMMV.
Hope this helps.
Cheers!