I’ve seen it happen to gpt/efi as well.
but its not about deleting grub.
It could be fixed even by passing some arguments to (admin) cmd in windoze.
It was more along the lines of hijacking the bootloader or boot order … grub just needed to be fingered again… maybe I can find the command somewhere …
I beileve its something like this, depending on the actual path of course:
bcdedit /set {bootmgr} path \EFI\Manjaro\grubx64.efi
please dear reader do your own research on this as I havent had to do it in a while.
EDIT. Heres an article that seems to cover this … again, I havent heavily verified it.
(scroll down for the windoze section)