I don't think you have much to worry about. While Samsung and the carriers want to hype that they are selling a ton of the Note7 (for a variety of reasons including getting bandwagon and people who want the latest new thing) its highly unlikely that they would sell 250,000 let alone 500,000 of them early on. Some people will wait to see how non-reviewer reviews and testing goes before buying, and a ton of people will forget to submit (or give up in frustration at submitting) for their free item (that's why companies have these online forms and mail-in-rebate forms, because they know lots of people will not go through with them). Also this promotion isn't open to the world. In the UK they get a free new Gear VR instead of the watch or memory chip.
It also says they could give customers a $100 gift card if they run out of the promotional prizes. I doubt many people here would want that over the memory chip or watch.