I'm sympathetic. The passenger, however, does not seem to be "deliberately causing delay", but is just getting off the plane. The passengers were allowed to get off the plane. Why? Apparently, they are permitted to do so. Perhaps whatever rule permits them to do so should be changed so they cannot get off the plane.
(By the way, if the airline and governing authority have so complicated the logistics there is a 45 minute delay in such an event, that is partly their problem. Why can't the ramp crew move faster?)
Suing is a dreary solution. The passenger might just instead feign illness, which the airline would have no recourse for. Seems to me that a policy change is warranted. Insist on having all members of a party traveling be together when checking in.
Perhaps the airline can ban the passengers from flying again, unless the airline is compensated for the delay. Losing the "gold card" status, or whatever, seems limp.
Also, if the airline can sue the passenger for deliberatley causing delay, the passenger should be able to sue the airline for deliberately causing delay, through:
1. not having full flight crew present
2. not having an agent at the jetway when plane arrives at gate
3. mechanics who are not ready, willing, and able to solve mechanical problems at the gate
4. not having a gate available for arriving plane
5. not flying faster in delaying headwinds
6. allowing passengers to carry on all manner of items in excess of stated guidelines