If I understand the setup correctly the outer 6 bolts connect to one part and the inner 12 bolts connect to another and all of the power is transferred through the flex plate. Correct?

If so, Arinuts, it looks as if there was only one bolt of the outer six still working. When the last of the flex plate finally split the engine would be unable to provide power to the torque converter then then on the the transmission. There may not be any additional damage done as long as the engine did not overspeed as the flex plate parts are all external to the engine itself. But the failure in his case was probably going to happen soon.

Cervan, assuming minimal flexure almost all of the force is being exerted along the plane of the flex plate. That they last so long already would indicate that it is sufficient for the purpose. In this case the failure point was not really in the overall plate but where the too small bolts attached it on the outer points. This would allow the plate to shift slightly and produce wear over the long run. I would not be surprised if the bolts were not properly torqued either.