I would guess the balance sheet of FFX is not affected at all by...

I would guess the balance sheet of FFX is not affected at all by the demerger.
Any new raise money would go into the new company. There wouldnt be any sale proceeds to increase FFX balance sheet.

The benefit to FFX and us as SHs would be we would now own a percentage of the new company AND it is now funded to proceed to construction(by the new partner).

I wouldn't get hung up on cash. I don't think this deal will be about cash (for FFX anyway). It will be about what % ownership FFX retain of the new company and what amount of cash the partner pledges to pump into the new company.