He was pretty adamant about his faith in the SLC LDS Church, going as far as to say he would still have joined the Church if the Priesthood Ban were still in place, and that if the Church reinstated the Priesthood Ban he would stay an active member.
This was 4 years ago.
Yes, I would have joined had the ban in place when I was alive. If the ban were reinstituted tomorrow, I would stay. The priesthood ban says nothing about the truth or falsity of the Restoration. Truth is all I care about.
I wonder what happened to convince him there was more truth elsewhere? He also expressed some quite strong views which, if taken seriously, were bound to find the LDS truth claims wanting.
I think Moroni's promise is more an invitation to experiment on what the Book of Mormon says, not to seek a spiritual experience. As Alma says earlier in the Book of Mormon, you need to think about it and weigh its claims against counterarguments and see if it is more plausible than not.
The existence of God is an empirical question that should be decided by experience, induction, and abduction; our feelings have nothing to do with God's existence or non-existence. Feelings are not good enough to justify belief in anything; we should only believe that which we have evidence for.