So my T43 lost its partition table upon reboot, again. It took me too long to find the note where I had jotted it down; next time, it’ll be easier to just search here.
sda1 1 ... 13sda2 14 ... 4864
The recipe is to re-boot the machine from the rescue DVD, use fdisk to write a new partition table. Reboot in rescue mode, let the rescue system mount the “old” system, chroot into it, run grub-install /dev/sda. Reboot again.(Yes, that can be done more elegantly, but I don’t want to remember all the lvm commands.)