Nothing, wait and see, if the plant puts out new growth, a lot of broad leaved evergreens lose their leaves around this time of the year, rhodies, mahonias etc. so just wait and see, ceanothus is drought tolerant plant, so try to plant it on a mound, so it can have some drainage.
I planted a new ceanothus last month. which was in flower. It has finished flowering now but the leaves are turning yellow. Where I live we have had very sunny weather and not much rain so I have watered regularly. It is near an east wall so gets sun from mid day. What can I do about the yellow leaves.