Wondering about deleting entire save

If the save file for my profile were to be deleted so I have no saves for Borderlands 3 at all, would my GR go back to 0 or remain where it is?

Remain where it is. It’s stored separately from your save files, but the file it is in also contains all your heads, skins, bank, keys, …

I’ve been reading that clear cache would make GR go to 0, is that true? Have glitched GR rank and just wondering if there is anyway whatsoever to fix that or is it just permanently stuck where it’s at? lol

As I noted above, you’d lose a lot more than just GR if you cleared the file that contains it, so unless you’ve done very little in the game it’s not worth it. Best thing to hope for right now is that it can be addressed in a patch in the not too distant future.