Hi Grxmyeli
welcome to the Appole (user-to-user) Community!
Re: "How can I get all my music that I downloaded that are gone"
You might want to check you have enough storage space on your iPad for the music files:
How to check the storage on your iPhone and iPad - Apple Support
If you don't have a back-up you can restore from:
Then you can likely redownload purchased music:
How to: Redownload music - Apple Support
Trouble-shooting if needed: What to do:
If there's an issue when you redownload apps, movies, or other content from Apple - Apple Support
If needed: Music Support Webpage: (Info. / support / contact options):
Music - Official Apple Support
All the best :-)