Ticker--who ran a business for years and knows his way around--has a handy little guide to contract law at his site.
It is important to remember that NOT ALL CONTRACTS ARE "WRITTEN." Some are oral agreements. Most white- and pink-collar workers have oral contracts
So when your tricky-dickster "Catholic" hospital chain says 'refusing the vaccination is considered to be a voluntary resignation,' they are kidding you and themselves.
...Both parties must agree to the same terms; that is, what is offered and what is accepted must in all material respects be the same thing or there is no contract. In most cases one party provides money, but not all; it is perfectly legitimate to contract for a case of beer in exchange for mowing your lawn, as an example. This is called "a meeting of the minds." If all parties involved did not agree to the same thing then there is no contract. That which was not contemplated at the time cannot be unilaterally inserted by either side later on....
Most hospital employees did NOT contemplate a vaccine mandate at the time they were hired. In fact, most hospitals themselves didn't.
Consult with a lawyer, of course. But make sure you get FIRED. Don't just meekly walk out the door like a good little sucker unless your lawyer says so.