I wouldn't worry about the bad message to other operators at LCY, it was pure fantasy to believe anyone else would switch. Skywork was a special case - too small to stay at LCY profitably but also operating a route that others couldn't touch. There isn't anyone else like that - Sunair benefit from the BA link and if they did move elsewhere they would be slaughtered by the lccs. The Dundee route might be achieveable if/when the PSO is up for renewal.
SEN needs to stick to what it does best - entice EZY to base a 4th aircraft again, resurrect the DUB link, maintain the BE franchise routes and look for opportunities along the lines of Adria.