28 miles to the gallon is good mileage to have a bad sensor up to that point.

If you had work done on the car before your trip you might just want to check the connections fit up.

It may have jostled off. Also if you know where to check it, checking it can confirm it has ohms of some kind and at which end it may be reading.

I would think, the ECU would think, its very cold and run very rich but if its off all together, the ECU might know the difference and throw the code for that reason.
It's an "emissions" thing at this point and with the "shotgun blast code system" it may be another tiny thing.

If it's running fine, I think your plan will work out except it may run a little different when its gets colder at altitude. There will a 12 to 15 degree change for sure!

Phil