I do not know how this happened as I did not really install new OSs or messed with grub.
For no reason, today Leap has disappeared from the boot menu!
I have two harddisks.
The main drive /dev/sda1 has my OpenSuse partition. It is encrypted using luks.
The second drive /dev/sdb is not encrypted and has an old broken Fedora installation that I no longer use and some data.
I tried using rescue disk to boot the system, but it does not even detect the opensuse system (because it is encrypted?)
I also tried mounting it with cryptsetup in rescue console and running grub tools, but they do not even find the opensuse again (through everything is there, I can see it with ls).
Also, looking at grub.cfg in the opensuse partition , I see no opensuse listed.
Please help! This is really killing my productivity.
It seems that nothing even detects (yast in rescue mode, grub-mkconfig, etc) the presence and bootability of OpenSuse, though all detect the old broken Fedora.
Is complete reinstalling the only viable option here?
So far you did not provide any factual information that would allow even attempting it. We do not even know whether you are using legacy BIOS or EFI boot, nor whether you are using btrfs (in which case previous instructions to mount root were likely incomplete).
My bios had both legacy and EFI enabled. Fedora used EFI and OpenSuse used legacy.
Well, if for some reasons your BIOS prefers EFI boot over legacy, this sounds like the very reason. You need to check BIOS options to chose legacy disk boot.