Aren’t there several realistic scenarios ...

Scenario 1

Emergency on board ISS. 1) One aspect of the emergency (e.g. noxious air) has incapacitated many of the crew, including all the ones trained to operate Starliner. 2) Another aspect of the problem (e.g. electrical faults that are expected to lead to fire) leaves no doubt that evacuation is essential.

Those ISS crew who managed to don emergency breathing apparatus quickly enough now move the incapacitated Starliner crew to their seats, strap them in and exit Starliner (closing the hatches on their way out), before proceeding to their own vehicle(s).

Scenario 2

Serious MMOD strike upon a docked vehicle, causing damage that makes it very unlikely to be safe for its crew to return in, and also at significant risk of posing a danger to the ISS.

Wouldn't the least bad option be to command an uncrewed undocking and hope for the best?

Scenario 3

During a flight test, a spacecraft is able to dock with ISS, but only after encountering significant problems. The first job of engineers is to consider whether it is sufficiently safe for the crew to return to Earth in, in the event of an emergency. Their decision is either 'no', or 'barely'.

An alternative provider of crewed LEO access services, known for its proficiency and speed of operations, announces that they will be able ready to send a replacement vehicle by the time of a suitable launch opportunity in 4 days' time.

There are no spare docking ports.

Scenario 4

Well, consider various lesser versions of Scenario 1. What if the crew was only partially reduced in their capabilities?

Perhaps they were both suffering from the symptoms of carbon monoxide poisoning (including headaches, dizziness, and confusion). Or perhaps one was serously injured, and the other was fine but needed to focus all her attention on tending to her crewmate?

Then it would come down to the question of just how complex and time-consuming the required manual step(s) are. If there's just a big red button that says "TAKE US HOME" then, it shouldn't be a problem. But we don't know.

And if there was just a big red button, couldn't they try bypassing the current 4-week delay, by coming up with some ways of pressing it without humans on board? ;) Shove an astrobee in there and give it a try. If it doesn't work, no harm done ...