What if that "elsewhere" is other infrastructure? Personally I feel HS2 is a solution to something that wasn't a problem. it wont take many passengers off the west coast main line as most dont travel the full route. they travel partial routes.
If we wanted to move Freight off roads and off passenger lines then custom freight lines could be built, with no need for high speed we could have built them at a fraction of the cost. that would allow more passenger trains on the existing line and free up motorway traffic space.
Personally though the money would have been better spent building a better fast line between Liverpool->Manchester->Leeds->York->Newcastle. Actually start to build this northern powerhouse they keep mentioning.
That being said, if this does get cancelled, odds are the momey will vanish into thin air rather than be spent on "better things", in which case I think it should be completed ( to the original spec, not the overground line through Manchester ) as something is better than nothing.