First, investment in California government debt instruments will dry up.
Second, the question which has been lingering for nearly fifty years is whether the judiciary can order tax increases (there was an interesting case in Kansas City schools on that issue many years ago).
Third, can a judge and/or his representative order spending reductions? The D.C. case may shed some light.
Fourth, the chances of the California government getting its act together (slim to none).
The role of the judiciary will be interesting should events continue in their current direction. Generally, it would be up to the state supreme court, since it is a question of the action/inaction of the state legislature. In that case it may come down to the wording in the state constitution.
If a state fails to support a federal mandate, there may be a question that federal courts can take up. Medicaid services might fall in this category, since half the money come from the state for the federal program. Of course, the feds could step up and cover the cost of their mandates, rendering that issue moot.