We've been here before
You can either take the view that the industry is on its arse (it isn't) or that there will be a slow down, highly likely.
People will not stop flying anymore than they will stop driving, sure they'll fly a little less, but the med routes are safe, because people are used to going there, have property there or access to property( probably why Ryanair have opened base in ALC & AGP) however the people who will still travel wont put up with Ryanairs crap customer services level and can afford to pick and choose.
What will decline is the travel to places you've never heard of because it is so cheap it would be rude not to!!
If i knew what oil was going to do i wouldn't be doing my day job, but its unlikely to stay above $100 for long and i suspect that a year from now (depending on who gets the white house) it will be nearer $80 which is still too much, flights at £29.99 base price rather than £9.99 or £19.99 are still afordable.
So a slow down yes, but if you start your training in late 2009 or 2010 you should be coming out around the time the people who could/should have retired at 60 are reaching 65 and by then we may be back to a normal business enviorment.
At what point to start worrying? well if FGS go tits up that would be a worrying sign but not terminal, if Jet2 go under then i would delay at least a year ditto the likes of baby, the rest should be ok but smaller
good luck