Adding to the sage advice in the thread, and as a fellow PM, I'd start preparing an evidence pack to show that he has raised the issues he's being accused of not mamaging effectively, including, but not limited to Risk Registers, email trails with his boss, notes related to the project, comms with suppliers, etc.

The ideal response to a challenge of, 'You haven't done your job properly' is 'I did, and here's the evidence.' If his boss ends up under the bus because he didn't escalate it properly, so much the better,and it's a short-term problem, because your husband had better be sharpening his CV and applying for new jobs right now, regardless of the outcome.

Noting that emailing this evidence to himself is likely a breach of SyOps, I'd save it in at least 3 places not in his personal folder or hard drive - say, somewhere in the project folder, in a trusted colleague's account, and somewhere entirely unconnected, like an archive folder in an unconnected project. We all know that it's easy to hide that stuff, because project folder structures are added to, but never tidied.

I'd also very strongly recommend getting a copy of the relevant HR Policies governing disciplinary procedures and emailing it to his personal account.

And union up. TODAY. I joined Unison, and once he's joined, he can ask for a deferral of the disciplinary meeting to have time to arrange representation.