In my experience, unless yogurt is fuzzy, or has taken on an unnatural tint, it should be fit for human consumption still. If it's past the point where that is an option for you, I'm sorry, I don't know which of your alternatives is the best use.
Just a thought: isn't putting dairy into
compost usually not recommended because of how it attracts animals? I think watery yogurt in the garden might do the same thing.
Sorry if that's not very direct advice, just my two cents!
