Agreed, the trick is determining when they are going to fall off the cliff and then move on the year before. They didn't appear to draft a replacement this year so I think they each get a 'real' year tacked on to their contracts with a few extra years to make the numbers work.
Po has been quiet lately and appears calm, so my guess is Knox gets done first, then Poyer to make the cap numbers work. Truman is on a prove it year. He either gets a mega extension, tagged or a thank you for your service meeting after this year. At the least, the Bills get a max effort season out of him as he tries for the mega deal-he may even hit the right hole this year once or twice.