A person can only get partner-sponsored temporary work visas for two years in total. As you will see here
http://www.immigration.govt.nz/migra...milystream.htm it says this.
If you have been living together for 12 months or longer, we may grant you a work visa for up to
a maximum of two years.
(my bolding)
The next thing your partner can apply for is partner-sponsored Residence.
http://www.immigration.govt.nz/migra...ly/default.htm (PR is a different visa a person can qualify for after living in NZ as a resident for a minimum of two years, demonstrating commitment to NZ.)