User blog comment:Master Sima Yi/Assassinews 05-08-'14 – Assassin's Creed: Rogue announced/@comment-25281081-20141007022031/@comment-1888015-20141007191759

I'm pretty sure they did mention that all co-op missions could be done solo, but the difficulty would be a lot higher than with a team. Granted, they were using Brotherhood missions as an example quite regularly, but wasn't it said somewhere in the Heist trailer?