Firstly the 146s will not be staying on the route, regardless of who operates them. The Saab 2000 does not have the capacity since it only has 50 seats unless the IAC are willing to go onto a 5 aircraft program which includes the spare but I doubt that very much since parking at SCS and the general logistics become more complicated. Loads in and out of SCS can frequently exceed the 50 seats that the Saab 2000 has.
A colleague of mine was speaking to a FlyBe cabin crew member during the other week who was under the impression that the IAC contract was a done deal! The Dash 8 Q400 has the performance for a 1200m runway and FlyBe have apparently indicated that a big announcement is likely soon!
The official line is that no operator has been chosen but everything points to FlyBe using the Dash 8 Q400!