Looks like they did some reassuring testing for the worst case scenario:

  The Avcoat blocks, which are about 1.5 inches thick, are laminated onto a thick composite base of the Orion spacecraft. Inside this is a titanium framework that carries the load of the vehicle. The NASA engineers wanted to understand what would happen if large chunks of the heat shield were stripped away entirely from the composite base of Orion. So they subjected this base material to high energies for periods of 10 seconds up to 10 minutes, which is longer than the period of heating Artemis II will experience during reentry.


  What they found is that, in the event of such a failure, the structure of Orion would remain solid, the crew would be safe within, and the vehicle could still land in a water-tight manner in the Pacific Ocean.