Your last paragraph confuses a few different things.

The aircraft was completely legal to fly under IFR during the en route phase. There is no requirement for a local altimeter setting for that; center can provide an area altimeter setting (and does so on every handoff).

The lack of a local altimeter setting precluded the use of the instrument approaches (the way you transition from en route phase to landing). Both of the instrument approaches are "when local altimeter setting not received, procedure NA". That equally applies to the RNAV(GPS) and ILS approaches.

That doesn't make filing or flying a flight plan to that airport under IFR NA; it just means that you have to either cancel IFR or fly a visual approach (which, despite the name, is an IFR procedure). Both are legal and commonly done; you can even file an IFR flight plan to an airport that doesn't even have a published approach or to a point in space that isn't even an airport.

When the pilot asked for a visual approach, they were taking on the obligation for navigating to the airport and for terrain and obstacle clearance.

Smaller item: KSRR is a non-towered airport. All the relevant ATC contact was with Albuquerque Center, not with a local tower controller. (If there was a local tower controller, they would almost certainly have been able to provide a local altimeter setting, making the instrument approaches fully available.)

ILS-24: https://aeronav.faa.gov/d-tpp/2607/06922IL24.PDF RNAV(GPS)-24: https://aeronav.faa.gov/d-tpp/2607/06922R24.PDF

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gpm an hour ago | parent [-]

Yeah, sure, you're right, and good point about non-towered.

Are you suggesting however that "The flight crew acknowledged the clearance and responded that they would cancel IFR “in just a couple of minutes.”" meant the crew was informing the tower that they would transition to VFR? That seems... unlikely. I'm reading the paraphrasing here as towards declining to cancel the ILS approach they previously requested because it doesn't particularly make sense to me otherwise.

Which is really back to "this preliminary report doesn't, and doesn't even attempt to, assign blame or contain sufficient facts to do so".

	▲	sokoloff 35 minutes ago \| parent [-]
		(Per other comments, a visual approach is still an IFR operation; they were still IFR, but flying a visual approach.) It's very common to cancel IFR in the air, especially for late night operations to non-towered airports. (At an airport with an operating tower, they will close your IFR flight when you land.) At a non-towered airport, you have to either call on the phone or use a radio relay to close your flight plan, which can be a pain, so in benign conditions it's very common to cancel IFR in the air where you have line of sight [meaning good comms] to the ARTCC radio transceiver and avoid the hassle of bad cell phone coverage and/or no radio contact possible on the ground. (There is no radio relay at Ruidoso; the nearest RCAG is at Roswell, 50+ nm away with terrain in between.) ZAB ARTCC's transmission that "they could cancel IFR in the air above 9,000 ft msl" tells the crew "once you get below 9000 MSL, you probably won't be able to talk to us on the radio". When the crew said "we'll cancel IFR in a couple minutes", that's also common. It means "we're going to stay IFR and fly the visual until we're a little closer and landing is reasonably assured."