I do find it hard to think that on those routes exited by Flybe at LGW where there is now an alternative on offer with either easyJet or BA, passengers would opt to return to Flybe from a different airport, LCY & presumably pay a premium for the privilege.
If Flybe are planning to re-position themselves with more of a premium product then the switch to LCY makes more sense. Certainly their existing fleet mix suits LCY but BA will doubtless fight to ensure their continued dominance at the airport where they now have a stranglehold.
I wish FlyBe well and hope that the switch from LGW to LCY, if it happens, works out for them but I have my doubts.