Do I have to buy that again?

I downloaded Gta5 on my Xbox 360 and now I have the problem that I accidentally deleted a file and to get it back I think I have to download Gta5 again.

And now to my main question: will I get my money back or will I have Gta 5 for free the next time I want to download the game or do I have to buy it again?

If you bought the game through the store, you can download it until Microsoft closes the store. If you bought a key, you can download the game again in the download process. In both cases it's free, you've already paid for the game.