Unfortunately you are right ... and I should have known better, because the update already failed once on me. However, it seems it only deleted its EFI-Grub in

Unfortunately you are right ... and I should have known better, because the update already failed once on me. However, it seems it only deleted its EFI-Grub installation so it should be quite fixable. But yes for an easier experience it seems that reinstalling normally proves a lot easier.