There's been no announced release date for the next patch. Also, you can't continue an ironman game in a new patch. But, once the new patch drops, the current version (1.25.1) will be leaded in Steam as a beta version, which will allow you to roll back to the current version (through the betas tab in Steam) -- just don't open your ironman game before rolling back to the current version. See this thread for instructions:
https://forum.paradoxplaza.com/foru...patch-level-of-europa-universalis-iv.1009270/ (note that you can't do this ahead of time -- you have to let the new patch install and then roll back to version 1.25.1).