The answer lies not in the past, but in the future.
Businesses, like lives, can be rebuilt on a platform of integrity. No one is in a position to say that John could not do that, those that do say so, say a lot about themselves. He may not, or he may.
Time will tell. Some will never forget, but Johns future is not in their hands, its in his.
I've read most of the threads and felt the intense hatred and anger out there. If I'd been ripped off I'm sure I'd be angry too, but all that aside... if HP survives this, and rebuilds goodwill with a whole new customer base by giving them good cars, backing up with good service and honouring fair warranty work... the cars still have the potential to become legends and collectors items. There's no doubt he can make a super product.
There may be others who can match his quality, but no one holds a candle to his marketing ability. The big money doesn't suffer fools lightly, but nor do they care about the past, they care about now and their personal interests. If HP caters to them, it could do well, and good luck to HP if they can pull it off - it'd take a bunch of guts. No one else has stepped into the gap in the public eye, and until they do and over-shadow HP cars, the posibilities are still there for him.
Personally, I think he has a chance. You can't build a crap TT1000 without it showing up really quick. Nothing like 1000hp to show up some flaws. If those cars stand up - its a big endorsement. There's one or two others out there who may offer a limited warranty on 1000hp, but they'd be holding their breath.... any engine can pop at power levels well under that and just one would hurt the builders bank more than a bit. I know it'd make me careful building one.