JMs, even after established, need consistent moisture. The brittle branches are dead but do a scratch test on other parts of the tree. Scratch the bark with your fingernail. If the tissue just below is green, that part is alive. If brown or hard, that part is dead.
One of my potted JMs lost its emitter last summer and I was pretty sure it was dead. But the entire tree leafed out this spring! Don't give up on it.
