First option - if this was a formal disciplinary meeting your husband should be informed at least 48 hours ahead of the process, reasons, provided with a copies of evidence and given the right to be accompanied
Without doing this, the worst they could do at the meeting, is inform your husband a disciplinary process will commence and set the disciplinary hearing for a later date. Your husband should not allow any disciplinary meeting to take place without being notified, prepared or represented
Because of your husbands length of service such a process requires 2 or 3 formal meetings over a period of time before a company could move to dismiss for performance related reasons.
Its not your husbands responsibility to document the outcome and agreed actions of a PIP. If the company is looking to escalate to a performance based disciplinary they would need evidence to justify it. If they haven’t recorded the PIP actions and outcomes, then your husband could easily argue any subsequent disciplinary process is baseless.
Second option could be they want to hold a without prejudice conversation to avoid all of the above and offer a settlement.
Third option is they want to discuss something more informal such as a change in role or circumstances, close off the PIP or theres a new matter to inform him about.
My advice would be that you have time. Treat the meeting as a way to gain information, listen but don’t agree or give anything away until your husband can take advice