I have read most of the threads which were posted in the Technical support forum during the last few days and the people there (mostly AndrewT) are very helpful and are able to solve most of the problems that the users have. I'm pretty sure that your rolled back version can be made to start(e.g. by starting eu4(.exe/.app) directly).Oh, contact support, I'm sure they'll be helpful to you and thousands of others.
Many of the issues with the new version only happen in very specific circumstances which testing probably wouldn't have found.