I'm declaring one of my startups kaput and moving on to another. The first venture, Stronico Contact Management, was an llc and had a ten percent partner. We declared it closed by mutual agreement and haven't spoken in a few months (everything is very amicable).
As I launch a new venture (going totally solo), do I need to formally declare that the old venture is null and void, and that I no longer have any business relationship with the original partner? Our partnership agreement for the LLC did not say anything about future ventures.
do I need to formally declare that the old venture is null and voidYes.
You will have to file Articles of Cancellation for the LLC in the state(s) that your LLC is registered in. If you don't file the Articles of Cancellation with the state, you'll still be required to pay any annual fees and taxes required by the state to do business in that state, even if you are no longer actively using the LLC to do business. You should be able to easily find the appropriate form to file on your state's website.
As far as being able to conduct business under another LLC, you are free to do so. There is no implied connection between you and your ex-partner in any future ventures.