If you do not do either of the Temple quests,
No matter what you do in the game, the Temple-O-Shadows' gate will open after you get back from teh Spire, I believe...If not, it DEFINITELY will be open once the game is beaten.
Also, it isn't possible, to my knowledge, to own both of the Temples...There are two quests you have the option of doing(before teh Spire)...The Temple you eventually have the option of owning depends on which of the two quests you choose...If you do neither, you can get NO temple...You can never have both.