First of all, talking about whether something will "kill" a hobby is not a productive question. It's impossible to destroy a pastime within the lifetime of people practicing it. It is possible for a pastime to reach a minimal level of participation to the point where it has no significant foothold and there is no motive for commercial growth or technical development.
For example, many Victorian parlour games aren't "dead," but you can only play them among a very small group of hobbyists. There's no interest in those games as living pastimes. They're antiques.
To give you another example, board wargaming is not dead, but many of its releases occur exclusively as part time affaors with nonprofessional production values. Several games only exist because of the interest of a rich baseball player: Curt Schilling. Advance Squad Leader is only in print because one rich guy wants it to be. Board wargaming isn't dead, but you can't say it's in fine health.
And guess what: They were mugged by RPGs. And while they went through their decline, board wargame enthusaists made exactly the same arguments about how the activities were separate things, etc, etc.
But all that's required for a decline is the following:
1) The new activity appeals to the same segment as the old activity.
2) The new activity occupies a significant amount of time.
I don't know about the Wii, but as far as RPGs go, this has already happened a few times. RPGs aren't dead, but they aren't the same, either.
