simple answer
simple thing is the engine will windmill a little until feathered
any reciprocating internal combustion engine is only around 30% efficient, therefore the other 70% goes in heat...... and the requirement to turn the engine and keep it going.
so if fuel runs out..... no bang no power, just drag......
and a supercharger takes 50% of the power it creates to run itself... its the law of conservation of energy, you don't get something for nothing!!!! - a turbocharger uses wasted energy (heat out of exhaust) to drive a compressor, so it is grabbing some of that 70% waste and using it to increase volumetric efficiency, that is the ability to induct the same air volume as the capacity of the engine
If you want to increase volumetric efficiency over 1, you need forced induction...
anyhow.... a windmilling piston engine that is supercharged may give some MAP but not much, as turbocharged engine wont give any MAP as there is no heat coming to run it..
Cheers
Dash