I read up a little on fixing XP and indeed there is the repair option from the disk. My concern was that Windows will overwrite grub as usual and you just confirmed that I will need to re-install grub. If I mess it up, I won't be able to boot into anything, except perhaps XP, if that gets fixed in the process. At the moment, I mostly use Linux Mint and very rarely boot XP to use Excel.
I found this tool which I will try tonight:
http://www.supergrubdisk.org/rescatux/
Apparently, it can also address my Manajaro error (kernel panics):
Maybe the kernel can be loaded but its initrd stage isn’t able to find the final device root filesystem (Kernel panic – not syncing: VFS: Unable to mount root fs. (initramfs))
This option tries to fix this filesystem errors even if the filesystem seems to be clean and ok.
