The House (or Business) that Jack Built...Succession Planning for a family farm or business

Planning for the future: family farms/ business

What are some options for dealing with a family farm or business when the person who built it or has been operating it for the last 20 years dies or wants to retire or transition?
If the business will pass to the next generation, how do you divide interests, roles and responsibilities?
If only one or two members of the family want to continue being involved, how do you provide for the others financially?