Often there are contracts. Sometimes for a very long time, often multi-year. There are sometimes escape clauses (like a morality clause for a spokesperson), but these aren’t easy to invoke.
I suspect many of them are up for annual review/renewal, when they can be terminated without penalty. It might also just be an attempt to get better terms.
They each have their own protection detail. Each will quickly move to protect the one they are responsible for, which will mean separating them (probably by a lot of distance).
Someone under SS protection can choose to waive it. There are some former presidents who deemed it unnecessary later in life.
No idea about the rest of your hypothetical