Love the ‘patootie’ reference!
I think that the OP’s question falls into the same category as the one about flying from Bombay to New York without re-setting the DI. What will be the indicated heading after 14 hours? Who cares?
Still, it might be useful to be aware that in a remote northern area, without an updated QNH and experiencing continuous significant stbd drift, that the aircraft will be descending with a constant indicated altitude.
I wish that your comment about “all aircraft being on the same QNH” was true in the UK! Unfortunately, what with low Trans Alts, Regional Pressure Settings, QFE and unregulated IFR being possible in Class G, there is a real possibility of two aircraft at the same level having different settings......