No expert on this but would expect that any cash received would be distributed to share holders just as stock in MHE will be distributed. Don't think that MHP can "un-ring" the bell. The company has said that share holders will get one share of MHE for every three of MHP held. Anything other than giving the share holders their due would result in a tremendous battle. Maybe such a deal would result in a tender offer for MHE AFTER distribution of stock.
The paragraph below is from an Oct 10 Reuters news story. I can find a couple of references on the web to this scenario. At the moment I believe they will sell outright if a bid is acceptable, because I cannot find a reference to other than a "planned spinout"
"McGraw-Hill, which is running the auction as an alternative to its planned spin-off of the business, wants to get more than $3 billion and could still decide against a sale if the bids fail to meet its price expectations, the people said this week.
Other private equity firms that submitted initial bids this summer, such as Thomas H. Lee Partners LP and Providence Equity Partners, dropped out because they felt the asking price was too high, according to the people familiar with the matter."