Jetavia's approach is certainly interesting, but many of his criteria, though relevant, leave room for subjective judgements.
My own subjective judgement is based on three criteria: the clarity of an airline's strategy - I feel that airlines that pick up and drop routes quickly, or carry out their strategy in a half-hearted manner are in danger; the extent and commitment of its financial security; and finally the strength and effectiveness of its total marketing strategy (including livery, identity, name and visibility).
On this basis, my survivors are ( of those with which I am familiar):
1. Ryanair
2. Easy Jet
3. Jet 2
4. Wizzair
5. Monarch Scheduled
The almost certain failures are:
1. MyTravel Lite
2. FlyBE
3. Air Polonia
4. EU Jet
The questionable ones are:
1. Volare
2. Sky Europe
3. BMI baby
4. Thomsonfly/Hapag Lloyd Express
And those about which I don't know enough are Air Berlin, Helvetica, GermanWings, Virgin Express, Sterling, Germania, and the others on Jetavia's list. It does seem inevitable though, that at least one of the German operators will fail sooner or later.