I understand the open ended part but I am not sure if once all BTCs are mined if the contracts will continue. It is my opinion at this point in time that the contracts are only for mining available BTC.
I should send an email to Genesis Mining, but I will wait until they catch up to their support requests and answer my last ticket. I hope my contract will continue beyond just mining available BTC and then be used to process network transactions.
I would be interested to know the answer too. Very good point