Self answer: the PGP boot-time password screen executes from MBR, and not from any partition.
Windows native System Image - what didn't work
I booted from Windows System Repair CD and simply restored the system partition, not touching my data partition. On reboot the PGP password screen was still shown, and after accepting password it displayed "Missing operating system".
Chances are that fixMBR would allow the system to boot, but I didn't try it.
Windows native System Image - what did work
I booted from Windows System Repair CD and selected to "format and restore entire disk", despite the fact that image contained just a single boot partition and did not contain my data partition (D:). System booted successfully, both the system and data partitions had the proper size, but the data partition was re-formatted. I needed to restore it from separate backup. Obviously, both partitions were unencrypted, but there were no complaints or leftovers from PGP, and I've been able to re-encrypt whole disk back to original state. Success.
Casper Secure Drive Backup for PGP WDE (3.0.2216)
Surprisingly, the tool only allows partition-to-partition backup. This works (amazingly fast), and I've been able to boot from the copied partition even if it was on an external USB drive. Still, the partition-to-partition scheme becomes troublesome when you want to keep a number of previous backups. There is no sign of the partition-to-file mode.
Lenovo T410, Windows 7 SP1 64-bit. The first disk partition 70 GB for system, the second some 230 GB for data, no "extended" partitions, no GPT, no dynamic volumes, no linux. Both partitions are encrypted with PGP 10.1.2 SP3.