Microsoft seems to be the best one at frustrating his customers!
Same for me here: long customer from Nokia Symbian and user of the Nokia/Ovi/Here Maps, I bought a Nokia Lumia only because I wanted to keep having these offline maps. Initially, the Drive+ app exclusive on Nokia WindowsPhones.
Now, Windows 10 Mobile is just coming out. Here Maps won't be there.
BUT Microsoft own MAPS is supposed to replace it completely.
The big issue is again the big step behind in features. Actually, Here Maps on my old Nokia E71 had more features than the one on my WP8.1 Lumia 730!
Will we get one day (and when?) the full Here Suite equivalent (Maps, but also Transit and Drive+ that made the benefit of the platform) on Windows 10 Mobile ??
Some says, not before Redstone, the next W10 major update.
Since then, many old MS customers may have just change the platform!