if you ask me, i reckon its a route that couldn't really work in the first place - a £5 departure levy (although ridiculous) is certainly not going to affect a route that is profitable. It would reduce costs by 0.34% if it was reduced to zero.
But, it is reason enough I suppose for an airline to withdraw from an airport that gives it narrow margins at the best of times so guess the management should bow down and scrap the charge.