A resident visa granted with no Section 49(1) condition (see above for Kelerei's explanation of that, and I agree it looks as though your friend doesn't have any) does NOT expire. Residence is for ever while the person is in New Zealand. It is the "travel conditions", a strange name for permission to re-enter NZ after being away, which expire after two years, but if the person is IN the country, that expiry makes no difference to their status.
Full Residence without conditions gives the holder the right to live and work in NZ at whatever they want, skilled or not, or to drop out and do nothing (if they've got the means to support themself), or to start a business, or be a student at domestic rate. (There are restrictions on how long a person would have to be in NZ before being eligible for state support, or a student loan, though.) The requirement to be in a skilled job is to make the person eligible BEFORE the issue of the visa. Once the visa without conditions is granted, they are not restricted.
Eligibility for PR does not include any requirement about work, EXCEPT as involved in fulfilling Section 49(1) conditions if the person had any.
https://www.immigration.govt.nz/new-...anent-resident