They end up as 'magical mystery tours' due to a/c maintenance issues and a general shortage of crews. The training system is designed to 're-educate' those from outside. Read into that what you will.
'Week on/week off' happens pretty well on the UK based 400F. Tis but a pipedream for the poor Classic chaps. There is some conjecture about the future of the old girl who is dodging the abbatoir at the moment because of sheer shortage of newer airframes.
Nuff said