One week after disaster struck, Glenn (the friendly neighborhood admin for my ISP) has restored my MT database files from backup tape. I’m running again.
A quick post-mortem: what happened to me was similar to what is described here. However, running db_dump -r did not successfully recover the data, which is why I needed to go to tape backup.
Now I need to spend some energy getting the data into MySQL so I don’t get burned by this again…