No it doesn’t. His loan is the same no matter what SPY’s value is. He pays it by depositing money he earns from his day job, not by selling shares. If SPY crash

No it doesn’t. His loan is the same no matter what SPY’s value is. He pays it by depositing money he earns from his day job, not by selling shares. If SPY crashes very hard his broker may force him to pay the loan very quickly, either by adding more money or by selling off his shares to cover the loan.