With regards to replacing Knock, what about Aer Lingus. Could route either LGW-NOC-MAN and return or DUB-MAN-NOC and return
Or if Aer Arann took over the route, it could always be as Aer Lingus Regional. Might need an extra aircraft in the franchise deal or something else would have to be cut elsewhere
Another option not mentioned - Ryanair. Would need a w pattern but they are very defensive of their position in Ireland and the idea of a stronger replacement than baby on MAN-NOC might not go down too well. So a pre-emptive move to start the route could always be possible