Will dead CPU fry motherboard?

I built a system for my parents based on comments at THG four years ago. It seems to have been a victim of a recent lightning storm. (It was plugged into a battery backup for that very protection, but this came through the phone line, DSL modem and apparently the onboard network card.)

The system failed to power up so I bought them a new PS, but they could not swap it out and took it to a "professional". This individual diagnosed the MOBO as the power problem. After relating to my mother a bunch of information I know to be false, this individual claimed that if the CPU was also bad, it would short out the new MOBO also. Thus, he told her, the CPU needed to be replaced as well. I'm a bit skeptical that this "professional" knows what he is talking about, based on inaccurate information he has provided on other issues and what seems to be an outlandish claim. I'm hoping that this community can steer to me to conclude that this statement has validity or that my suspicions that he is trying to make an extra buck are true.

Thanks,
KBoyKool