Some confusion here I think. The York-Shrewsbury and return were worked by three separate locos in each direction. A diesel, typically whatever was available, worked from York to Stockport and waited there to work the balancing service. Any electric could be used between Stockport and Crewe with the two trains normally crossing on that stretch so two different locos. The Crewe-Shrewsbury leg would be another diesel which would then work Shrewsbury-Wolverhampton legs of Euston services later in the day. The opposite principle covered the northbound working. The loco "exchange" between the York-Shrewsbury and the Euston-Piccadilly sleeper would have been an electric unless of course the OHLE was switched off for maintenance.
However such diesel haulage of the sleepers would have been more likely on Saturday night/Sunday morning workings when the TPOs didn't run. I did once use the Euston-Lime Street sleeper on a Saturday night to find on arrival at Lime Street a 47 on the front and the train in reverse formation. I found out later in the day that the train had been diesel hauled from Crewe via Chester with a shunt around the triangle at the latter point.