Walnut Slabs & Trapped Moisture

Welcome to the forum, Rich - we're glad to have you here with us. What part of the country are you in ?
as for "long term", that is a big variable in different parts of the country.
Arizona = very short, but, in Florida = could be months or a year.

in a humid area, such as the Lower South East, it could become a structural nightmare. Inviting in a host of things like termites, powder post beetles, mold, rot, etc.
Out West - I have no clue as to the long term effects of trapped moisture in wood. Hopefully, someone "in the know" can answer that question.