Even developers with the best of intentions can run into serious construction problems. It is a gargantuan task to build a high rise, with the potential for complications possible at any point during the process.
If it's the seller who refuses to close, the purchaser must either accept the return of the deposit or pursue an action for specific performance, by which the purchaser asks the court to order the seller to perform and transfer the property.
Manhattan just doesn't behave like the rest of the country when it comes to residential real estate activity. To prove my point, I peppered Noah Rosenblatt, of Urbandigs.com, with questions about sales activity in Manhattan.