You've said a few things now which make me think you haven't read the docs though. Liverpool's forecast average loadings for HS2 is in the 80%s for its 2 classic compats.
So they won't be full then?
With a 90 minute journey loadings of over 100% are tolerated elsewhere on the network.
Additionally that assumes they retain the 200m CC sets with merges, but since you have essentially removed the justification for any other 200m set destinations on the West Coast (by eliminating the Wigan junction) there is no reason to select that train length.
You can follow the example of TGV Atlantique and build the train sets to the same length as an 11 car Pendolino.
This is compares to Leeds and Manchester's 400 metre captives of mid 40%s. It's all in the docs, and as I've said above means in my book from Manchester and Leeds one or two trains a day running as 400 metres (where they'll be 60% to 70% full) and the rest of the day running as 200 metres (where they'll be 30 to 40% full).
This makes numerous assumptions, none of which are actually supported by the available documentation - for instance that fare based suppression of journey counts will continue despite all need to constain demand being removed. (The reason this decision is made in the documentation is to be ultra-conservative, when noone actually believes that will be what happens).
Captive trainsets at full length don't actually cost very much extra to run than 200m trainsets, especially if it is a unitary 400m trainset that has more than double the number of seats but only the same crewing and pathing requirement.
If only one or two trains were to be 400m long, why on earth would we expend ridiculous resources on building so many 400m long platforms? If train capacity is not going to be any higher than classic lines why would we even bother with TSI compliant platform lengths?
There was never any real possibility that the majority of trains would be operated at 200m length on Captive routes - the costs of changing train lengths in service are greater than simply running the longer trains at all times, especially in the era of demand managed fares.
This is one of the reasons SNCF occasionally proposes 400m long TGVs on Sud Est but then realises it has no money for such a thing and shuts up again.
My trips to Liverpool, on the other hand, look like they will be spent standing, unless some way can be found to couple trains together.
Since you are removing a large fraction of the traffic on HS2 by removing the Wigan and Manchester sections there is no capacity constraint so you can make the liverpool train whatever length you can cram into the platforms at Lime Street.
If you haven't read the docs, it's no good guessing at business base. The bit away from Crewe to Wigan had a key purpose for depot reasons which no longer exists.
The primary purpose of the spur was always to provide the setup for HS2-3 to Scotland and also to actually alllow HS2 to be used for something beyond the Y network.
The depot was just a happy coincidence that allowed the use of a cheaper site in a more deprived area, producing more jobs to buy off more opposition.
If that has knock on effects for the bit to Manchester, complaining to me isn't going to alter that. But I don't think it being run by two 400 metre classic compatibles is going to have the drastic negative effect you seem to think, especially if the money can be used to better all round effect.
It won't have effects, since the only evidence we have for it being cut is a clickbait article in a local rag/on its website.
Two 400m classic compatibles will add half an hour to the journey time and add another five minutes to the average wait period compared to the current service.
You end up with Manchester gaining only about two carriages of seats per hour and only saving 20 minutes.
You might as well axe the entire Crewe-Birmingham section in that case as it becomes essentially worthless.