Simon tried to scare off other bids by making yet another minimal bid for GGP. In the end though, greed will win out and others that recognize the full value of GGP will not be intimidated by SPG or their shennigans.
There are many fish in the sea much larger than Simon. A significant buyer with large capital resources would be a nightmare situation for Simon. Bolstering the #2 competitor to Simon would further fortify an already formidable competitor.
The only way out for Simon is to buy GGP. Other scenarios could be devastating.