Maze's End
The win condition is part of the resolution of Maze's End second activated ability.
Playing the tenth different guildgate isn't sufficient, you still have to activate Maze's End (remember that you don't necessarily have to find something with the ability, just that you control ten gates with different names when you finish resolving the ability).
Technically, Maze's End won't be on the battlefield at that time, that's just because returning it to your hand is part of the cost to activate the ability.
Daniel Kitachewsky
L3, Paris, France
Rules NetRep