This is the ultimate guarantee that Light could have had before going to the meeting.

First, have a corrupt government official die a few days after the meeting to prove that the third Death Note is real.

Then, write the names of politicians in ascending order of importance: start with low-ranking officials, move up to ministers, and save the presidents of smaller or less influential countries for last.

Once imprisoned, Light could simply bluff that he had a partner with a third Death Note. He could claim that if he wasn't released, the killings would continue, with even world leaders becoming the next targets.

To make the bluff more believable, each victim could simply leave a threatening message for the next target before dying: "Release Light, or you'll end up the same way."

Honestly, I think this would have put governments in an impossible position. Even if they suspected it was a bluff, could they really afford to take that risk?

Let me know what you think.