I HIGHLY doubt Cedar Fair walks away and sells all of it. A split that makes sense to me is if it is negotiated that Cedar Fair sells off a chunk of parks and becomes the "midwest park chain", where they effectively rid themselves of any major competition whatsoever. Keeping Valleyfair, Michigan's Adventure, Cedar Point, King's Island, Dorney, Worlds of Fun, and Canada's Wonderland (proximity wise makes sense, I doubt SEAS has any specific interest in one foreign park). SEAS would get KD, Carowinds, the Schlitterbahns, Knott's and California's Great America. This makes it so SEAS only has one large scale regional competitor in Six Flags (of which they offer a vastly different product so they don't really compete very much) and the obvious scattered local one offs. The parks they get make sense for their philosophy going forward as well, with Knott's being their example of how they want each of the other parks to get (though it will be tricky having both BGW and KD serve as large scale destinations, realistically the two would compete with each other and limit the other too much, interesting business convo to be had there).
Obviously this would come with a price decrease, and something like this I believe circumvents the shareholders moreso than an entire acquisition (depends on the details of the structuring of their shareholding), though it would be possible that rebranding of these parks would have to occur to a degree to clearly separate them (get rid of the flags, can't use "King's", etc.) SEAS would only be strengthening their foothold in 3 of the 4 areas they actively compete in (CA, TX, VA). Only new market would be southern NC, which they can easily establish as a year round attraction of a higher investment grade than Carowinds currently is.
Keep in mind it is very common for business offers to overshoot what they really want as a form of making the "compromising negotiations" fall closer to where they really want to be. I am sure SEAS would gladly take the whole bag, but I highly doubt there is anyone in the SEAS boardroom that would say "no deal" if parks like Worlds of Fun, Valleyfair, and Michigan's Adventure were pulled from the deal. Ultimately, they don't lose much in not getting the crown jewel of Cedar Point either, since they are effectively trying to turn all of their parks into the massive destination Cedar Point is. It would be a slow suffocation of what is left of CF as SEAS gradually grows their empire to be destination parks in areas never thought to be a destination, and SEAS would probably end up buying the chunk CF kept in a few decades for even cheaper than they would get it now.