A few weeks ago, I had an interesting case with Trip.com and MU. My flight was delayed by an hour due to flow control. I applied for an involuntary refund on trip.com (really because it was a red eye and I did not feel like taking it anymore), and they said they sent the request to MU, and the deadline is after the flight departure. I contacted MU, who said they did not receive any, but confirmed that the invol refund is applicable.

For some reason, after the flight departed, trip.com rejected the refund, so I contacted them again and attached the screenshots with the MU chat, and they resubmitted the request, which was later accepted and a full refund issued.

As per moondog's concept, in stage 3, what you can do is ask Trip.com to negotiate with HO to issue to give you something, most like in the form of trip coins. It helps if you booked the trains, hotels and the WUX air ticket with them ofcourse.