I'm not worried either, but I will say that if Donald didn't think he could pay this back, he would be an absolute lunatic to enter into this agreement. It reaches far beyond Madrox and into all of the other group entities like SJD etc. He wouldn't just lose the club, he'd lose £20m+ on top and it effectively makes it a personal liability to some degree. They wouldn't be getting the club for £9m, they'd effectively be being paid anything above that sum that Donald owes (currently in the region of £20m).
Like GOM, I can't see a schedule of repayments, but I would be extremely surprised if it's onerous or short term. Like I say, this is not an agreement you enter into lightly as the terms are very very harsh if he doesn't pay up.
Upshot, however FPP come on board, it probably isn't via this agreement unless Donald goes bankrupt.