Update: Ubisoft has announced it will postpone its plan to pull some of its older titles offline until October 1. The firm also stated that Anno 2070 will not longer be taken offline.
The firm initially said that 15 titles would be affected by the removal of online services, meaning that online features, DLC, and multiplayer modes would no longer be accessible.
Now, according to Ubisoft, the single-player DLC of several games on PC - Assassin's Creed Brotherhood, Assassin's Creed 3 (2012 release), Far Cry 3 and Splinter Cell Blacklist - will be available to download and keep before October 1. If you own these games on PC, activate your DLC before the decommissioning to continue playing it. There will be no impact to the same single-player DLC on consoles, and you will continue to be able to download and play them after October 1 rolls around.