Needs a clause to prevent you from conceding.

If you concede, you leave the game first, thereby removing yourself from the purview of all continuous effects that might have applied to you, then you lose now that there's nothing that can replace it.

Still, it's entirely too easy to throw away all your life on something like Hex Parasite, or if you're that worried about being stuck on an odd life total, Plunge into Darkness.

Did I ever tell you about the time my opponent cast Mindslaver and I looked down in my hand and saw a Wall of Blood? I didn't win that game.

Why not "If another player would win the game, you win the game instead."? From what I understand, a player only wins (fairly) by removing every other player from the game, so this effect wouldn't apply if you were the last person knocked out. But if the player were to use something like Helix Pinnacle or Laboratory Maniac, then that could be used.