I agree with Prefect. This is not a question of SISU's ability to pay the rent or whether there is a business case for moving to Northampton. In my opinion, their game plan has been, and continues to be, based on the assumption that they can financially distress ACL and buy the Ricoh on the cheap. They have been single minded in pursuit of this plan and no offer from Hoffman or the Fans will deflect them from this objective.
As for the FL changing their minds if the fans raised enough dosh to cover the rent, unfortunately wingy, I don't think there's any chance that they'd do this. Apart from anything else, if the FL do anything to undermine their plans, I believe that they are concerned that SISU might take legal action against them. Some people have speculated that SISU have some sort of legal case against the FL because of an error they made with the contracts/player registrations/golden share some time before Ltd. went into Admin.. If this is correct, then it means SISU have, (and will continue to have), significant 'leverage' in any negotiations with the FL.