The issue with off-line Diablo is - unlike the original Diablo II - once a map is uncovered, it is uncovered even if you restart the game… Which takes away the replayability.
If the maps would regenerate in Off-line mode like it does in On-line mode - I would definitely be playing Off-line.
I am a solo player being forced to wait through the queues just so that the game is replayable.
Playing online with someone you know, essentially doubles your storage space.
Does changing difficulty not work?
Interesting idea… I hadn’t considered that. But I’ve got from 128 to 24 in the queue this hour… I’m not giving up my spot 
u can reset it i forgot how tho… i used to do it on LOD/plugy cant remember how tho… would be nice if it was a toggle option cuz sometimes single player i do like the map there
Just change difficulty, the maps will auto regen.
Its been awhile, but its possible that in one of the newer Plugy’s it was a built in option.
It works the same as in original D2. The map remains the same until you change difficulty.
You reset maps by just changing difficulty. Join Normal, leave, now your maps are reset for NM and Hell.
There is a command-line argument that will accomplish this, without having to switch difficulties.
-resetofflinemaps
Depending on which method you use to start your offline games, you can either:
Add the argument in the “Target” field of your D2R.exe shortcut. After the closing parenthesis, just type a space and then the argument -resetofflinemaps (don’t forget the dash).
Or, if you use the launcher, start the launcher, then click on the gear next to “Play” and choose “Game Settings.”
Once that window comes up, you will see a check box for “Additional command line arguments.” Click that, then type -resetofflinemaps (don’t forget that dash) in the box, then click “Done.”
This will give you a new map at the start of every game.