Hi VSPECT,
I think regardless of the issue, i tend to agree with most that it would be very difficult in getting the workshop to claim responsibility. (unless there was a clear case of neglect)
Id hate to be a tuner as generally they have a pretty hard job. (This is definately one of those cases).
One thing which might come back to bite your friend is the fact that he installed the parts himself. (I assume he is not a qualified machanic).
Also a bigger turbo, cams and fuel pump were installed without upgrading injectors or ecu which could have also caused problems.
Its never nice when a engine goes but hope your mate gets it back up and running.