It is generally assumed that Deke Slayton would have assigned Gus to the rotation
so that a Mercury astronaut would have been the first man on the moon. To make
that prophecy come true, all successive missions would have had to have been clean
of problems and the LEM would have had to have been finished on time.
It's really a fruitless point to speculate on, however. The sad reality is that
the Apollo 1 fire extended the timeline making Neil Armstrong and Buzz Aldrin, the
first men to land on lunar soil. Sad in that three men died horribly in order to
prove that the system was going awfully astray.

RDG