The N2 Pro has a feature called loop recording. This means it keeps recording until the memory card is full, then it overwrites the oldest video clip and continues in a circle, so to say. So the larger your memory card is, the more video retention you have. I would not use anything less than 128GB in an N2 Pro, which gives you around 11 hours of history.
If by your question you meant use the dashcam's display and menus to view existing clips, no they are not deleted just by viewing. But when you watch, there is an option to delete.
Once the microSD card is full, the camera will automatically replace the oldest files with new files in a loop to allow continuous recording.
Note that locked files are protected and will not be replaced, you must manually clear them off the microSD card when they are no longer required to avoid the card filling up with only locked files. To avoid the card filling up and thus preventing new recording, this option can be turned off.
With current firmware, the camera can take up to a 256GB MicroSD card. That should get you... 18-19 hours of footage in dual-1080p mode. That's enough to get you through even the longest days without recording over older the oldest file. When you get home, transfer the footage to a hard drive, reformat the card, and watch the footage on your computer.