After 9/11, Virgin decided to ditch 25% of capacity, that being their guess as to how much the market would decline in the short term as a direct result of the WTC attack. Spookily enough, most majors with heavy exposure to the North Atlantic/US market came to a roughly similar conclusion. No other European carrier had such a large bias towards the US as Virgin did, and therefore Virgin was particularly exposed to how that market reacted.
To achieve that 25% reduction, VS axed the B747 Classic fleet. Of course, this was the only aircraft VS flew with Flight Engineers, so the redundancy list at one point approached 40% of the flight deck staff, as all the FEs were to go!
As history and hindsight now shows, even with the extended effects of SARS shortly after 9/11, 25% was an over-estimate of the effect on Virgin's market (though it was considerably more than that on some routes), and the job losses never got anywhere near the 25% proposed - except for the dear old FEs. Even some of them got a reprieve, as two Classics were retained for the MAN-MCO task.
That's the history lesson. The most salient factors in job security at VS are firstly that the airline is far less exposed to any one market than it was in 2001, and secondly that BALPA rapidly became a significant strength in the workforce, ensuring (after a shaky start) that the correct principles of equity, seniority and process became enshrined in the company's redundancy policies.
No airline is secure, and airlines funded by private equity are less secure than those with government backing, but VS is in good shape these days and is as likely as any middle-sized airline to be here in another 22 years.