Let’s say a few of the MCU villains succeed in their plan:
- Ultron gets his ultimate body, destroys Sokovia
- The Shield/Hydra heli-carriers become airborne
- Killian assassinates the US president
- The Chitauri and Loki set up base in NY and the portal remains open
- Cross begins mass production of the Yellow Jacket
- Zemo decides to revive the winter soldiers
The heroes are either in disarray or eliminated, so each of the villains and their followers decide to take out each other. Which one is the last one standing? Which one causes the most casualties? Which one is likely to team with the leftover heroes?
Just to clarify: Sokovia is destroyed via meteor fall from AoU. If Ultron wants another city meteor, he'll need to build another one.