Ime there is no "immediately" w/r/t off-loading luggage. Thankfully I don't have much experience with this, but I've been on board several flights where off-loading someone's luggage became necessary, and in every case it's taken at least one extra hour.

Most recent example, in late October, a flight I was on was delayed for more than 3 hours overall because an elderly woman and her companion were unhappy with their seat assignments. The situation apparently escalated after pushback, because the plane was returned to the gate and the couple was escorted off. After a good bit of discussion, the captain decided they not be allowed to fly, and the wait to offload their luggage began...