When you upgrade, I think it resets as you are a year 1 captain, but one of the other guys should be able to confirm (been awhile for me so I can’t remeber)
The unpaid part is only whilst getting type rating. You aren’t employed by JQ until you return with said type rating. This is one of the reasons they don’t do their in house TR, because they have to pay you from the start (yes absolutely ridiculous, the joint is run by the HR guru’s, they even have an in-house TR approved) so you end up with an ok type rating that luckily you didn’t have to pay for, the downside is you don’t get paid during that time.
If you upgrade, you are already employed so you are still on the payroll. It’s only the intial entry into the company you don’t.
If you’re looking to live in NZ PERMANENTLY, then go for it, but don’t do it if you are trying to get to OZ or have aspiration of long haul/787