Even if he isn't, it would be an awful defense to have to present by TSCC, since an incompetent prophet has a good chance of rattling some testimonies.
Interesting question, especially considering the timing. If Monson is "unfit" for his summons, then he would also be unfit for conference the next month. We have seen the church basically wheel out corpses to attend conference so any lack of participation by Monson would cause major confusion. He basically cannot play that card
If he isn't fit to appear and answer questions about the summons, how can it be claimed he is fit to lead the Church? If the answer is that God will sustain him, then God will sustain him in answering questions about the summons.