Sarkus:
Possibility does not require occurrence. Otherwise a unique event could never be possible until it occurs? Rubbish.
It could never be known to be possible beforehand. Moreover, if it never occurs at all then it cannot be said to have been possible to begin with. There'd have to be some flaw in designating it as a possibility. Some innate contradiction which invalidates it.
Essentially: Given infinite space and infinite time, if something does not manifest ever within this time period and within this space, then it cannot be said to have ever been possible. The word would have, quite litterally, lost its meaning.
But it would not have happened at the precise time, with the precise identical make-up of every single thing in the Universe? No - so it defeats your argument.
There are three answers to this:
1. A situation similar to the ManY World's Theory is true. Every action spawns a distinct timeline when faced with a choice.
2. Possibility can be conceived as ignoring either time or space. That is to say, it can either manifest at a different time or in a different place. If at a different time, aeons in the future or elsewhere in space, the exact copy of you will go to the game. Given an ignoring of space, at this very moment an infinite copy of you are all ready going to the game.
Or 3. There is no possible, only the necessary. Due to a strict determinism, only those things which can be found in said deterministic system, can possibly be. Yet the source for this would have to be found that can invalidate so many acceptable necessities.
A further weakness to your argument goes as follows:
If you can prove that all possibilities actuallty exist - then you would prove that not only does God exist - but also that God does NOT exist - as both would be possible (through your original point I - in that if it can be imagined it must be possible....).
Presumably, the argument for God himself (which is not included in the ontological argument) would also demonstrate why its non-existence would be unimaginable but for ignorance. That is to say, one could not positively affirm that such could not be the case, but only assume such things.
For instance: Some might people claim they can imagine a square-circle just by referencing it. But clearly, this is absurd, as they can neither imagine it, nor base any reality on it. Thus it is not imaginable.
Also, more would rest on whether God is necessary or possible. If necessary, then the paradox could never come to be. If possible, then the paradox would similarly never come to be, as God would be one day existent, the other not. Both sides would equally manifest and equally fail to manifest at certain times.