I'm sure another operator will take up the slack and offer a route to London.
London has been served almost continually since 1985 with various different airlines such as Ryanair,Suckling,Manx,Euroceltic and Arann.
One problem though is if you want to attract the business traffic, then you have to base an aircraft in WAT to offer an early AM departure and evening arrival. This may be a prohibitive cost to many.
You also need an aircraft with good economics such as an AT72 or Q400 so you can offer low fares to compete with cheap alternatives to ORK and DUB.
I think LTN has proved over the years to provide the strongest London airport for WAT traffic.