Oblique cases and 'si quis'

Question

It is convenient to formulate conditions with si quis, for example:

Si quis me audiet canentem, non gaudebit.
If anyone hears me singing, they will not enjoy it.

Here the same unnamed person is the subject of the subordinate clause introduced by si quis and the subject of the governing clause that follows. If I want to change the role of this person in the subordinate clause, I can simply change the case of quis:

Si cui canam, non gaudebit.
If I sing to anyone, they will not enjoy it.

But I'm not sure what to do if I want the person to be anything but the subject in the governing clause. Two questions:

1. If I want the person to play another role in the governing clause, can I and must I add a pronoun? I'm thinking of something like: Si quis me audiet canentem, ei succurram. I don't seem to be able to satisfy myself with this construction without adding an ei.

2. Can I and should I omit such a pronoun in the nominative case? That is, should I have added an is or ille after the comma in my two example sentences above?

If there are any rules of thumb or similar ideas that might help with composing around si quis, they are most welcome.

Answer 1

I found this statement in an Oxford Latin Syntax Volume I, 11.137 "the anaphoric pronoun is":

For the anaphoric pronoun a distinction must be made between the oblique forms and the nominative subject...

Without ripping too much from the book, it effectively states that no subject is preferred if the subject is well-introduced, while if the well-introduced topic is in an oblique case, a form of is is preferred.

I believe this covers the clauses in question. I am not sure if the pronouns are a requirement, but it is explicitly stated that they are preferred for oblique cases.