Guest,
Can't answer the specifics of the RNZAF but a number of aircrew do transfer to the RAF.
Can you be given a ground job - indubitably?
Yes you sign for 10 years, they expect 10 years. There is always a get out clause however. The get out clause will be in their favour of course. It would start on day one as per contract.
Why might you be shafted with a ground job? Well you might be a crap pilot or have a medical problem. Your aircraft type might go out of service and it is cheaper, and more efficient, to train someone else who will give greater return of service.
Lots of jobs are 'flying associated' where it is deemed best practice to employ someone who knows what is what.
If you want a job just flying then join an airline.