تغديت؟ سأنصرف

점심 드셨어요? is small talk, not a nutrition survey. 네, 드셨어요? back is enough.

먼저 들어갈게요 / 수고하세요 is how you leave while others stay. 야 나 간다 is for a different building.

회의 있어요 buys you a closed calendar. Use it when it is true. Using it as a fake shield gets remembered.