Is there any precedent or legal framework to "what if" he had decided she was not capable and he wanted to take over?
Yes there is: Make a third announcement to see if there are 2 lawyers on board. Once you get an affirmative set up an arbitration room in Business class. Post that once solution has been arrived at send out a Whats app/ BBM verbal announcement to all on board to vote and based on the outcome of the vote draw up agreements as well as affidavits absolving airline, aircraft manufacturer as well as pilots form any and every litigation. Provide will making services and if possible video graph it so it is proved not under duress
Based on the above proceed with landing
For good measure lighten load by throwing out the Lawyers.