There are plenty of unsecured creditors besides bond holders, especially the specific bond holders mentioned. Plus it could be that the bondholders have assumed that the payout will be higher than they thought. After all, the merger talk has been going on for months and the price hasn't risen till now.
The bottom line is the unsecured creditors, and especially those holding bonds, are looking for the most per dollar in principal held. Nothing public suggests that it will be US at this point.