What would have happened if someone slaughtered the Pope in medieval Europe?

[Kgw]

Except that Pope was forced into exile/POW status and if I remember rightly died a natural death in Rome years later anyway?

Not exactly the same.

 

[Andre Bolkonsky]

but these were done by the Romans themselves. No foreign prince marched into Eternal City and stabbed the Vicar of Christ that I am aware of.

'The Roman Solution'.

There is a reason that phrase is synonymous with assassination.

 

[Geriander]

If you have the pope in your power you can probably arrange a poisoning or other accident. No need to publicly take the blame.