Life will find a way. Going back can be used to create nuclear winter but even then, life will go on.
To completely screw over the world, I would go into the future and acquire the source code for a general AI.
Then the world can be locked down and robots can be built to abuse every human and sentinent being individually, for a very long time.
Yanis Varoufakis explains the reasoning
What’s the line of reason? They voted according to their core values and since they have to pay for the implementation, they should change their values or should have voted solely by self interest?
Is the position of ‘the left’ that it is right to vote in self interest and not for the common good?
As a map some days ago showed, Canada, Greenland, Panama, probably Israel, maybe even Ukrain - it’s all about shipping lanes.
All that effort makes sense if there is the believe that global trade will increase and that the USA will still be relevant when the center of the global population is in Asia.
So extinction is not the goal but could be an accepted risk.
It depends on what Europe wants to be. The language is in some ways connected to the culture. Would Europe get a more Mediterranean savoir vivre if everybody spoke Spanish or French? I think so.
An ambitious and interesting option for Europe could be Arabic as the lingua franca. If Europe commits, other countries like Iran or India could also be interested in joining. That could create a huge area with a single language as long as it doesn’t splinter into dialects like the current Arabic.