I'll be honest here from a neutral look at this venture taking out emotion and other issues and just looking at the factual evidence unrelated to specific people in or out of the UP organization.
UP wanted for whatever reason (not debating this as it's irrelevant to the point) to restore a Big Boy. There are many logistical and financial issues with undergoing this. There are also to cost paths.
The first cost path was the restoration of the BB to oil fired with a full conversion of all systems. This would require manufacturing and procurement of all components with a cost likely well into the 10's of millions of dollars territory.
The second cost path as to gut usable components out of a successfully operating and very similar 3985 to convert and operate the BB. This path significantly reduces cost, time, and I believe most significantly risk to the venture.
We all know which path as chosen which brings me to my main point. The issues with the first path still exist if 3985 is to run again. There is also a compounded cost factor of operating not 2 but 3 steam locomotives for a company which is currently going through major cost reduction projects across the line. While operating even one steam locomotive by a class 1 RR is an anomaly, 3 is like a unicorn with two of those being large articulateds more like the mythical chimera.
From non emotional standpoint looking from the outside, one can see why as an organization UP would restore and operate in heritage what was their largest most powerful steam loco ever, one of the most powerful in the world ever, and will be the largest and most powerful steam loco in operation in the world. This brings me to my conclusion and prediction of two scenarios.
Both scenarios are that 3985 does not run again and instead is put on display somewhere with the 4014 tender repainted to 3985.
Scenario one includes running the BB mostly as a show using diesel power as the real motive behind it. This would greatly reduce operational cost, maintenance, and risk. 844 may or may not be run as often and will double head for big events.
Scenario two is much like one using diesel power however 844 gets quietly sidelined (basically retired) but kept in operational condition just in case of BB issues or failure. In this scenario 844 could come out as a BB stand in but again utilizing diesel for the work.
From what I see I have doubts as to whether to purpose of converting to oil was for full operation, or more because it was easier to source and fire in a way to create a show. This plays into a lot of what's seen in the process.