It is totally a poison pill deal.Seems like the potential options the CMA are giving seem like things MS are unlikely to agree to. It could be that MS tries to convince the EU to accept their terms and then pressure the CMA to agree to lighter terms, which is a stretch.
Since it's been reported that the regulators communicate more than they have in the past, it's possible that the FTC and CMA advise the EU not to agree to remedies from Microsoft that are too weak.
Also, it doesn't matter if any other of the three block it, just one of the FTC, CMA or EU competition authorities is all it takes for the kill, and if anything, we should expect the EU to just straight up shoot the deal in the face. The CMA was playing nice by giving terms that they know MS would never accept.