At some point, many small businesses cease to exist. Plan now for what that ending looks like. Yahoo Small Business provides some input on selling your business.
SCORE (Service Corps of Retired Executives) offers some tips to valuing your business for sale. The Missouri Small Business and Technology Development Center also offers answers to the question "what is my business worth?"
However you choose to exit your business, you will need to complete the appropriate steps with the state of Missouri. Check out the Dissolving a Business section of the Transitioning My Business page on the Missouri Business Portal.