The Leafs are now 7-3 without "the franchise". The 4 most important players are Andersen, Rielly, Marner, Kadri and Tavares. Did I forget anyone?
I would not put Kadri ahead of Matthews. Matthews in and Kadri injured would be an even much better team. You already forgot Matthews was leading the league after 10 games when he got injured.
Matthews in and Andersen out probably Leafs would suffer since Andersen playing like an MVP right now and Sparks is Sparks.
Matthews in and Rielly out would be interesting. They'll probably be just as good since Andersen is making the defense look adequate and Rielly is not really known for his defense but rather offense and Matthews is the better offensive player.
Matthews in and Tavaras out, well Tavaras plays better defense but Matthews has better overall offense so let's call it even.
Matthews in and Marner out, well this one can be debated one is a superior shooter and one is a superior passer.
Marner also kills penalties.
So I would say only Andersen is more important than Matthews. Andersen is the MVP of the Leafs. Kadri is last of these listed in importance.