For those of you wondering what exactly the "five day" letter is, don't worry, you're not alone. Apparently what the letter does is basically tells Seymour that he has five days to report, or the Raiders have the option of suspending him for the remainder of the season for not showing up.
However, it still doesn't do a whole lot to persuade Seymour because whether or not he shows up, he still gets paid. From where he's sitting, not playing (for the Raiders) but still getting paid, then entering free agency next year (of course, barring a franchise tagging) probably sounds pretty good.
Of course, there is that little thing of not being able to play. Whether it's for the Patriots or for the Raiders, a player wants to play. The last thing any football players wants to do is miss a game, much less an entire season. It doesn't matter whether it's high school or the NFL.
There's really nothing the Raiders can do at this point. This is all on Seymour. There's no language in the contract saying that the Raiders will get their pick back and the Pats will be forced to take Seymour back or anything like that, so it's down to two choices, both of which fall in Seymour's lap.
He can play, or not.
Make your move, Seymour. You've got five days.