Except it's only after escaping from the Misty Mountains that Gandalf can have any idea that Bilbo possesses such a ring, but I don't remember him modifying the plan in response to that knowledge. Meaning that if it was a suicide mission, it was set up that way all along, so rather than this being Gandalf the realpolitik puppetmaster it's Gandalf the Rollercoaster Tycoon player, erecting a lengthy and complex scheme just for the joy of watching the ensuing catastrophe.