Broken "Deluge" Quest line


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So I just finished rebelling against the king of Poland and finally got Radziwill on the throne. The problem is; whenever I ask any lord to give me a special task they tell me to deliver a letter to the king. Now normally this isn't a problem until we (or I) realize that by "King" they mean "King Jan Kasimir" the dude that I just finished rebelling against. SO, since hes nowhere to be found on the map this quest line's pretty much broken and I realized this after I had already spent hours on my character (Day 782) so of course I dont want to just start over.

Now my question is:

How do I complete or at least fix this questline without King Jan?