He has, in a bank, something like £300m or so. Everything else he's "worth" is tied into what he referred to as "wallpaper", or shares. As in, he owns 60% of Fraser Group, which gave him a valuation of around £3bn. He could use that money/capital to be creative, acquire stakes in businesses, like Evans Cycles, without spending a penny of his own cash. However, that's tanked to the point where he's not even a billionaire anymore and it's getting worse. Many stores will close, his online business isn't worth enough to support him and he's had to close Shirebrook meaning he can't even keep the online business open anyway. His disastrous PR will have lost a lot of custom and I personally doubt Frasers will survive this. Whether Ashley does is another matter, but he's likely to just bugger off a la Philip Green to some island somewhere.
So on to NUFC, who are different. They are a private company owned wholly by him. He cannot loan NUFC money from Frasers Group nor use their capital/share/value to support NUFC. So if/when he takes the club down - and he knows he will, because he's an inept and incompetent boob who runs things on barely even a shoestring - he simply will not have any cash in his bank to "loan" the club. We then enter borrowing which will be a) hard to get in the Championship, and b) expensive if we don't bounce straight back. It also goes against his business model and, importantly, his principles - he hates the City/financial institutions and cannot bear to be beholden to them.
He's basically got a bunch of absolute **** not just coming, but already here. He's worth less - by millions - every second of every day. He cannot possibly afford to keep NUFC. He stands to lose absolutely everything in 3 months. And everybody knows it. He has NO choice but to sell the club. None whatsoever. He's just very lucky someone out there wants to buy it. I suspect he'll have to take around £280m, which is still a little profit. But I honestly can't see how he could even contemplate keeping the club.