This article is also quite insightful. Lots of good stuff in there:
How phantom shares on Wall Street threaten U.S. companies and investors
I'm actually not so sure anymore that
@Artful Dodger is right. It sounds like a naked short sale is more like a futures contract. A purchase is agreed upon, but the actual delivery of the stock doesn't have to happen until settlement date. Thus, a person naked short TSLA never actually delivers a share in the first place, because it does not have a share to deliver. Thus, either the transaction fails at some point, or the short seller buys/borrows the share and delivers it.
Although after the stock split the naked short seller would have to deliver 5 shares, a run up in the stock price aside, it sounds like he could just arrange to buy/borrow 5 shares cheaper after the stock split, and deliver the 5 shares. It doesn't appear to be the case that a naked short seller will owe 1 share @ $1,500 and then another 4 shares @ $300 for a $2,700 debt total.