Yes, you can play the Division offline.
There are two ways to do it:
One is by playing co-op with a friend who has an internet connection and
The other is by using Ubisoft’s companion app on your mobile device.
If you want to play offline with a friend, all you have to do is start the game and then invite your friend via Play Together mode.
You’ll be able to access content such as missions, sidequests, world events etc. that are available in the area where your character levelled up after moving on from their storey progressions.
Ubisoft’s companion app for Division will allow you to continue playing when there is no internet connection or if it drops out during gameplay but only by using preinstalled maps which limits what parts of New York City players can explore without being online while still receiving rewards based off how much they’re contributing points towards either JTF or Cleaners factions.