The fact that you folks are getting a confusing dialog on upgrading grub-pc is bug 581760. I've uploaded a fix for that to maverick, which is awaiting release team review.
I don't think that this could have caused unbootability, though. Significant confusion, yes - but the grub-install diversion in lupin-support should have meant that things work pretty much no matter what you select in that dialog. Bug 604417 seems a more likely candidate for causing trouble here.
The fact that you folks are getting a confusing dialog on upgrading grub-pc is bug 581760. I've uploaded a fix for that to maverick, which is awaiting release team review.
I don't think that this could have caused unbootability, though. Significant confusion, yes - but the grub-install diversion in lupin-support should have meant that things work pretty much no matter what you select in that dialog. Bug 604417 seems a more likely candidate for causing trouble here.