Wait, what? That seems odd. They've deleted music videos from my account (which I had the files for, and the videos in question were also pulled from YouTube etc by the band, so I don't think it's apple's fault they were pulled), but I still have all the music I've made myself. I do back it up every 2 or 3 months (I would cry for the rest of my life if I lost it, I have nearly 2yrs of continuous music), but I've never had to restore it (and this has reinforced why I do back up).

Edit: looked it up, I see the issue now. I don't use Apple music, and every instance I can find of this happening is associated with ceasing that subscription. But I just use iTunes and the iTunes store. Dunno how this would work for you since it's your own music (and I dunno if it'd work for music not in the iTunes catalogue, ie stuff from Bandcamp, qobuz, cough cough less than legal methods, etc), but it would appear all you have to do is log in to your account again and re-download the deleted files.

Second edit: just realised I have lost some actual music from my account. The series of live albums that iTunes directly released from the iTunes festivals they ran like 15yrs ago just came to mind. They're gone from my account. And probably a bunch of others. They were never deleted from my hard drive though.