A bit off the topic but to reply to an earlier statement.
stevef
Hmmm... I guess that's why the P51 was eventually fitted with licence-built Merlins, then
Correct to a point.
It was the supercharger technology that made the Merlin superior to the Allison orginally fitted to the P51. It took the Yanks to refine the Merlin for mass production.
As much as Rolls Royce has everyone believe that they produced the finest engines, they were effectively hand made. Each piston individually fitted to each bore and each crankshaft individually fitted to each journal. You couldn't take a piston out of one cylinder and fit it to another. The Roll Royce produced ones are/were a nightmare to own.
The "Parkard" Merlins were a much better engine. True, a British design at the end of the day.
Back to the original question.
I would expect a supercharged engine to act in a similar manner to a normally aspirated one in the situation described in the question.
That is RPM and Manifold Pressure would not change or if so only momentarily, oil pressure would stay the same also. Temps would drop slowly and of course there would be some yaw and speed would decay.
Lack of fuel flow, assuming a flow gauge is fitted, would be the major indicator.