It seems what you are concerned with is the tax and penalty on the growth of current investments.
Yes, if you withdraw $$ from the 529 plan for purposes other than qualified educational expenses, then the earnings portion of the withdrawal will be subject to a 10% penalty and will be includable as ordinary income. It also sounds like CA will impose their own penalty for non-qualified withdrawals. But remember, the penalty and tax only occurs on the earnings, not the after tax contributions....and all withdrawals from 529 plans, like traditional IRA's, comes out prorated between earnings and contributions.
If you are certain you will not be using the 529 assets for qualified educational expenses, than it would be advisable to withdraw them sooner than later, as all future earnings are going to be reduced by 12.5% before tax.
No, you may not convert your 529 plan to an IRA. One is an educational savings plan, one is a retirement plan.
The above idea of transferring your CA 529 plan to another state without the state penalty, before making a withdrawal, should be investigated carefully....as the CA 529 plan may have provisions dealing with this....and the cost of the transfer may exceed the 2.5% penalty on the earnings.
BruceM