Although slow compared with the train, Metrolink tram will be a better quality journey than any "rail replacement bus" which are always a dreadful experience, taking forever to load and unload then following devious routes around one way systems and stuck in traffic jams, lurching and swaying on uncomfortable seats. I know the engineering shut down is necessary and ultimately will bring a better rail service but I do not pay rail fares to travel on a BUS.
From my experience in Greater Manchester:
The train fare from my local station is less than the tram and bus fares from the local stops.
The 'bus replacement' service is usually timetabled at 10 minutes less than either the tram or the bus from local stops, and regularly makes the journey more than 5 minutes less than the timetable allows, unlike the trams and buses.
The 'bus replacement' is often a coach with quite comfy seats, unlike the seats on the local buses and the tram (assuming you can actually get a seat).
So all in all, I'd say the value of the rail ticket for a 'bus' is quite good in comparison to the bus fare for a bus and the tram fare for a tram.
Is there a decent connection at Stalybridge to/from TPE Piccadilly services?
33 mins connection time (or 3 minutes if you are quick) currently going in to Manchester (from Ashton), 35 minutes (or 5 minutes if you are quick) in the other direction. From stations to Huddersfield it's 45 minutes going in and 16 minutes coming back.