“What happens to those in California who want to remain in the union??”
Same thing that will happen to anti-Brexit folks, and the same thing that happened to the 40% of the colonists that did not want to leave the King.
“Would those who want to stay in the USA be compelled to move to another state?”
No, they would have to move to the USA, at that point it will not be just another state, but another country.
“What about all the military installations in California? Who would own them and operate them?”
Please see Cuba or the Philippines for your question.
“what about citizenship? Would everyone in Calif. be a citizen of California only, and lose American citizenship?”
Eligible for dual citizenship, which includes dual income tax liability, like now with Americans working in other countries.
“What about California’s share of the national debt? Would the new People’s Republic of California cut a check rUncle Sam for that amount?”
Send them a bill. Response taken into consideration when figuring their credit rating and exchange rate on trade.
Countries break away all the time, what happened to the former Soviet states? Or Bermuda, or _______ fill in the blank?
If they plan to have no Soc Sec and Medicare like the Texan separatists want to do, it drives all the older folks back to the US, giving a much lower cost of government. It also provides a large supply of lower cost housing for the population as they exit and most sell their residence.