If they've already preemptively cancelled both Chieftains for tomorrow, then they really ought to want a unit stuck in Inverness to form Tuesday's service. It might require some diagram rejigging, but there shouldn't be three days of cancellations!
Why shouldn't there be 3 days of cancellations?
Is the line from Inverness to Edinburgh going to be open for 0755 on Tuesday?
Or, as is previous storms, are NR going to want to check the line (and others) to ensure the line is free from any debris.
The people planning all this and doing all the alterations know what they are doing (even if the public and forum members don't think they are).
LNER will have had many conference calls with NR Scotland, between them it will have been decided what service LNER operate.
Also, Hitachi units when they enter service get a 48 hour fitness to run.
If a unit went to Inverness today, and was planned to come back Tuesday, it couldn't come back as a passenger service as the FTR would have expired.
The unit stays in the station at Inverness and no longer goes to depot. And a FTR can not be done in a station.