Its happened so many times; I make a fresh wubi install and update it, and then on reboot I find myself dropped to a grub shell. I could never figure out why it broke, or how to fix it. Luckily, I don’t have to! Someone else has finally found a solution!
Turns out, its dead simple. To boot back into ubuntu just takes three lines on the grub shell:
sh:grub> linux /boot/vmlinuz-(Your version of the kernel) root=/dev/(Your Windows partition) loop=/ubuntu/disks/root.disk ro
sh:grub> initrd /boot/initrd.img-(Your version of the kernel)
sh:grub> boot
Then once you’re back in, simply reinstall the package “grub-pc”. No more reinstalls and losing whole configurations! I much prefer being able to fix a problem than simple admit defeat with a reinstall, and my hope in wubi was fading. Maybe this bug will be fixed properly soon, but in the meantime, at least i can work around it when it happens.