Let's say I'm running a mill deck. I have some kind of infinite mill combo ready and available (e.g. Semblance Anvil imprinting a creature, Myr Retriever and Grinding Station - this lets me sacrifice Myr Retriever to Grinding Station, retrieve another Myr Retriever, mill opponent for 3 cards, and cast a new Myr Retriever for free). However my opponent has two copies of Emrakul, the Aeons Torn in his deck. Since Emrakul shuffles back in to the deck each time it's put into the graveyard, this means I can't actually mill him out.
However, through repeated use of the mill combo I can in principle 1) figure out every card in his deck, and then 2) mill him until the last three cards in his deck are Emrakul, Emrakul, and [irrelevant card] (I assume here the number of cards in opponent's deck before I start the mill combo is divisible by three). This means opponent must hard cast Emrakul to win, and I already know (e.g. via Thoughtseize) that he doesn't have the resources to do this. So I win anyway by milling in three turns.
This kill will take a long time to execute, for obvious reasons, because each time I mill an Emrakul it gets shuffled back into opponent's deck. I'll need the deck to be stacked in exactly such a way that the two Emrakuls + an irrelevant card are at the bottom of the deck. This will happen eventually, just probably not for a very long time.
Question: can I actually execute this kill in paper, or will standoff rules kick in first?