he could even have the nvr at home ... then it will never be found

Yep, or in a locked room, in a locked box, down some dark dark stairs, through a dark dark door.

Much harder to steal then the camera.

Dvr linked to an output on the alarm and email notification. If the dvr gets stolen no problem. It's emailed you the picture. Could also email you open/closed images.

it will give some info granted. But if dvr theft is an issue and you cant protect you need to look at off site storage for all alarm images.

I believe the purpose of this install is for health and safety (lone worker) and not security so I would think 3 x IP cameras with an NVR would meet the requirements. Lone worker only required during open hours which is good lighting, etc.

Not sure what hazards face the lone worker in a 500sq ft office, possibly a thief? lol