There certainly seems a strong sense of doom and gloom around here and its justified to an extent, but we have to look at the wider picture - the economy isn't in a great way and if you look back through history, airlines jumping ship from STN has happened before and each time the cycle has reversed and things in the next peak have been better than the previous.
For example, quite a few airlines left around 95/96, mainly for LGW/LCY - such as Aeroflot, Cubana, Aviaco, Tarom, Air Engiadina.
Then a few different airlines turned up around 98, and 99/2000/2001 were quite vibrant....then there was a mass exodus post 9/11 with the complete loss of Star Alliance (don't forget there were numerous daily LH/SK flights at that time), Continental and others....2002 was pretty much just FR, GO and Buzz.
Fast forward to 2005/6/7 and you would turn up for your of a morning to see multiple Air Berlins, Eos, Maxjet, Germanwings, Transavia, Sky Europe, CSA, Malev, Norwegian, Globespan, El Al and others all out there. Few of those remain at STN now. But thats not to say some won't return in future. Lost routes also create opportunities for others.
It is also the case that each round of long-haul operations has been stronger than the last - first a short-lived AA operation, then a more successful CO effort that was killed by 9/11, then the all premium airlines which got killed by AA's second coming (but in fairness would probably have run out of cash eventually anyway given the economy - though they did last 2.5 yrs) and now Air Asia which seems certain to move to LGW but have been operating for some time now with excellent loads and supposedly good premium demand. Maybe long haul will be the driver of STN's next bubble - possibly FR's long-rumoured venture?
Things look good at LTN at the moment (I fly from there also) - but avid supporters should bare in mind that things could go wrong very quickly and shouldn't be keen to willy-wave.....EZY could have another spat and remove aircraft/routes, there is nothing to stop some airlines moving airports, and if a poor economy continues there is always the possibility that one or more airlines could fail.