Then everybody else would have to decide if the rest of the network still provides value to them, so a few more would disappear. At some point you'd reach an equilibrium where either a small portion of the original network is happy with what they still have for the money, or the whole network collapses.
It doesn't feel like people would quit because of the expectation that "everybody with any sense would stop using it". You could already say that now about FB, and you could definitely say it for many other products. Yet they are still used.
This question (can Facebook charge people to use its service?) is fundamentally vastly different from the one in the article, which basically is: can someone kill Facebook by buying enough people out of using it?
It would be a slam dunk lawsuit.
You can still offer discounts (airline tickets, Adobe, etc.) or negotiate pricing (cars, etc.) legally.
But, it is illegal to isolate someone and charge them more without justification as in OC's example.
So yes, Facebook charging a single person $1k/year is a true hypothetical. It couldn't happen legally in the US.
If Costco charges $1k for a bagel and gives it away to everyone for free except insists on you paying, that's a problem. You're not allowed to isolate discounts based on race, gender, etc. So Costco would have to have a pretty creative reason for making you pay and no one else. It wouldn't hold up in court and it would be price discrimination.
If it costs everyone $1000, there will be many many many people who cannot afford that.
If it costs only me $1000, I'd stop using it because... well I already stopped using it so I did it for free actually.
Second case, being the only one out (i.e. the black sheep) means you might consider paying for it to not stand out.
Source: I smoke, and about half the people I know do too.
If facebook costed everybody $1000/year, I would definitely stop using it, because the network would be immediately broken since everybody would know everybody with any sense would stop using it.
If facebook only costed only me $1000/year, I would know the network was still intact, and I would consider it.