Comment 4 for bug 51497

Once it crashes you can still configure the bootloader following the original community guide:
https://help.ubuntu.com/community/FakeRaidHowto#Set%20Up%20the%20Bootloader%20for%20RAID

Just change root to the installer target:
sudo chroot to /target

install dmraid:
sudo apt-get install dmraid

Then follow that grub guide I posted above, don't go further than "Ubuntu 5.10" as anything past that is outdated and not required.

I think this could be integrated into the grub section of ubiquity as its not much extra to work.