Thanks for your replies!

I should point out that as a permanent State Govt employee, I can't lose my current position - it waits for me to return. So no risk there.

I may also get the opportunity to have a different and higher position after the contract as it is based around putting in a new computer system which will need skilled support people once it's implemented. And they could be based anywhere (it's a state-wide computer system) Which means I could return at the higher salaried level to my home-town after the two years. But no guarantees...