On April 17, they official withdrew their offer to buy out SemGroup. Basically, PNG gave up since SemGroup didn't want to be bought and the market figured PNG would raise their bidding price.
Smartly, PNG decided not to waste money bidding against themselves overpaying and walked away. Since then, their stock has fallen 1%. Odd how the market punishes good decision making by management
Disclosure: I have no positions in any stocks mentioned, and no plans to initiate any positions within the next 72 hours.