When the originator receives a CacheNotFoundResponse and the cache is in degraded mode, the transaction is marked as partially completed, but the commit completes successfully.

I believe that is not correct, because the originator could crash after the commit but before the merge, and in that case the transaction will not be applied on all the owners. The transaction manager will ignore any commit exception in NON_XA/useSynchronization mode, but at least in FULL_XA/NON_DURABLE_XA mode we can signal to the user that the transaction may be lost.