Last time around (post 9/11) it was (if memory serves)
1:Those on unpaid leave
2:Those made compulsorily redundant
3:Those who took voluntary severance
4:New entrants as needed
They had however got hold of several 744's from an Alitalia order and kept a couple of the classics on. A number of those who left never came back, this was the start of the low cost boom. There was much expansion from 2003 until around the start of 2008.
Not the case this time. Jobs are much rarer and many are the preserve of 200hr "cadets" or those willing to pay so those who departed will probably return unless bonded on pain of death by stoning in the ME or something.At the end of the bond a lot may return and they will have positions reserved as they are effectively on unpaid leave.
Last time you didn't need a current type rating either. The world is once again a different and harsher place.