"Guests who should have checked out but haven't left yet" 或 "Guests due to check out but still remaining in the hotel" 都可以表达“应离店但还未离店”的意思。
其中，“should have checked out” 使用了虚拟语气，表示“本应该已经离店”；“due to check out” 表示“按预定应离店”；而 “haven't left yet” 和 “still remaining in the hotel” 则分别表示“但还没有离开”和“但仍然留在酒店里”。这两个表达都清晰地传达了原句的含义。