Crossrail 2 is something which needs to happen, along with the diversion of some WCML services onto Crossrail 1. HS2 will significantly increase the traffic at Euston, and the Underground frankly can't handle it. It also relieves pressure on Waterloo and on the Piccadilly, Northern and Victoria lines. Without Crossrail 2, HS2 can't happen.
While I agree that the possible cancellation of the Midland Main Line electrification isn't good, it's not a big problem in of itself. The line gets by as is, and could do so for quite a while longer without significant issues. Furthermore, given the work for it is upgrades rather than digging an entirely new railway, it has a significantly shorter lead time. Crossrail 2 probably won't be ready for 20 years, the MML electrification could probably be done in two. Yes it'll be delayed, but I'd still bet on it being complete before Crossrail 2.