They renew contracts at the end but there are some cases when they just terminate contracts, even before the end. In February they terminated contracts for few guys on 330 and after 3 weeks they called them back. Presently, they are terminating some guys on ATR.
Staff travel is a joke. Return ticket to FRA costs around 600$ (it's a standby ticket) and you can buy full fare ticket with Qatar or Turkish for about 700$ if you book little bit in advance. Sometimes you can even book full fare ticket with VNA for the same price.
Regarding flying, 330 fleet is the best one and it's easy life, flying around 50-60 hours