For example, if I have some type A struct { B string; C int }, and I have a func foo(a A) *string { return &a.B }, and I call it with c := foo(a), will a necessarily stay in context until c is collectible?
Or, if I define func foo1(a A) *string { s := a.B; return &s } will that have any effect on when the A can be collected?
In the first example, assuming a is not used after calling foo(a), a is collectable, because you passed a by value. The function returned a pointer to a value in a copy of a, so a becomes collectable, but the copy created in the function foo is not collectable.
Now, if you passed &a to foo(a *A), then a would not be collectable, because c is a pointer to it.
The second example you give also passes a copy of a, so same arguments apply. However, if you passed &a, and then returned a pointer to a copy a string from a, a would be collectible, but not the string you returned, because there is a reference to it.