1. Nobody can tell you an answer except INZ, and I doubt if the COs there know yet what the arrangements will be. Those will depend on what politicians decide, and at the moment, the government are concentrating on measures to deal with the epidemic, making immigration a low priority. Many individuals' concerns are just having to wait. When the emergency is over, there will be measures put in place, no doubt, to pick up the pieces.
2. Your sister's husband's partnership work visa is dependent on her worker's visa. If her visa is invalid, then so is his. If in the end she turns out to have to re-apply, so will he need to.
3. Unless your sister's line of work is in one of the essential skills
for this emergency, see here for the list of medical specialisms
https://www.immigration.govt.nz/abou...and-exceptions, she wouldn't get permission to travel anyway, even if THIS visa were valid, or she obtained a VOC (very doubtful at present as the INZ offices are closed). An offer from a different employer wouldn't make any difference.