REQ Help - SPOILER - Stormrider Ending Questions

[DudeBoyz]

I have just finished Stormrider and have a question about the
very ending of the book. It could be a SPOILER to people who
have not finished it yet, so if you do not wish to know the
details, please stop reading here.
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At the end of the book, Gaise Macon uses the Skull knowing that
Cernunnos will be able to take full control of him. But before
that final occurrence, Gaise has arranged to be shot by Mulgrave.

My question is, how was it possible for Mulgrave to deliver any
kind of killing shot at all given that the Skull had been
absorbed into the body of Gaise?

Secondly, how is it that the Skull appears to be destroyed? I
thought it could not be destroyed by any means that men have
access to.

Does the Skull still exist? Or are we to believe that a single
gold musket shot has the power to not only kill the body of the
host who has already absorbed the Skull, but to somehow destroy
the Skull itself?

I'd appreciate some useful replies that can help me understand
the ending. I'm not sure why these things aren't obvious to me
after reading the book, but if I missed something, I'd really be
grateful if someone could help point that information out to me.

Thank you