Is Mario still relevant? I think he's more at risk of falling further than Zelda.
There was all kinds of fandom going around with Zelda's anniversary, but what about Mario? Most of his games are party games or kart racing games, which are dime a dozen, on both the Nintendo and Sony platforms (Modnation and the recently announced Little Big Planet racing being strong competition). Games like Super Mario Galaxy 2 or Super Mario 3D Land were both complained about due to less gameplay and mostly repeating levels for the sake of gathering to add to gameplay length.
I think Zelda will be around for a long time. I just worry that Mario may be losing some momentum (we will see at this year's E3!).