In the late 90's the Matterhorn was reaching the end of its original lifecycle, and DL was faced with two options: a multi-year closure to demolish and rebuild the ride, or a long series of shorter refurbishments to replace the aging infrastructure bit by bit. They chose the latter and the ride was closed for about 4-6 months nearly annually for the next decade-plus. The annual closures have concluded, but its refurbishments are still more frequent and more in-depth than most other attractions. At this point, it's the "rollercoaster of Theseus," with nearly original element replaced and/or significantly rehabilitated over the years (some, many times over).
Even in the era of notoriously lackadaisical maintenance, Disney had the sense to see that the Matterhorn was worth maintaining and preserving for the future. In addition to being an icon for the park and a piece of rollercoaster history, it's also quite popular with guests and packs more into a relatively small footprint for a headline attraction (about 60,000 SF for queue, loading, two ride tracks, maintenance, theming and a portion of the Monorail, compared to nearly 200,000 SF for Epcot's single-track Guardians coaster). It's difficult to imagine that modern Disney would be capable of fitting something that checks that many boxes into a footprint that small, making its replacement difficult to justify, even on a spreadsheet.
While it's always been a relatively rough coaster (at least by Disney's standards) the new ride vehicles installed in 2012 with individual seats made it significantly worse. Among other issues, they have a higher center of gravity, so instead of riders being cradled by the banked turns, they're flung to the sides. Additionally, the shape of the seat often leaves guests in more of a supine position than sitting upright, so every bump and fault is felt through the tailbone rather than absorbed by the tush. Simply replacing the vehicles with ones more like the previous versions would do a lot to both improve the ride experience and to dispel the notion that the ride is being neglected.
Of course none of this is to predict future actions (particularly in an era where there seem to be no limits on what could be removed), but Disney's commitment to the ride thus far does not indicate they're looking to replace it in the near/medium-term future.
They would likely just rebuild the coaster and mountain so that they are two separate systems rather than the combined one they are now. This might require a little more space, but they'd likely just take up some more area to the north and east (though I also assume any eventual rebuild would coincide with an eventual usage of the Motorboat Cruise area and ultimately sub).
The existing coaster is already two entirely separate ride systems, though they intertwine throughout the mountain itself. It's not unusual for one side to temporarily close while the other continue operations. Even the ride vehicles are slightly different and permanently installed on one track or the other, so that CMs checking seatbelts on the 'inside' of the tracks are always on the same side as the buckles.
Sleeping Beauty castle colors have changed a few times throughout the years. The Matterhorn stays consistent minus some fluctuations in the amount of white/ snow.
The color of the mountain itself has also varied over the years. Originally it was grey, and then at some point (likely during the 1978 overhaul that added the abominable snowman) it changed to a more peach/pink color that more similarly matches southern California's mountains than the Swiss Alps. The grey color returned during the 2012 refurbishment that covered the mountain in scaffolding for the first time in decades.
