I very, very much doubt that the Wii is selling primarily to the demographic that wants to play Red Dead Redemption, and thus this game will mean the end of the Wii. Those kind of people are already on the HD console bandwagon.
The biggest strengths of the Wii are currently:
- lots of software that's attractive to children. There are a lot of children, and they all get consoles these days. The Wii has the most toy-like appeal, which matters to parents who generally buy them.
- Nintendo Software. Nintendo have grown into being the current undisputed king of casual game developers, thanks to a thorough understanding of the interplay between hardware and software innovation, and 'what casuals want'
None of these things have anything to do with games like Red Dead Redemption. Bully 2 would have been a bigger threat, or perhaps if Rockstar had managed to create RDR as a game suitable for kids under 12.
The real threat to the Wii are without a doubt the new motion controllers. If paired with decent software, then families will be able to choose a HD console and be able to satisfy at least a large part of the Wii's attraction, i.e. the party games / Wii Sports type affairs. And the added features that the camera offers will help.
However, stealing back Nintendo's current mindshare will take years, and some significant missteps on Nintendo's part. Nintendo has a lot of cash now and they are in an excellent position. It's up to them to mess things up.