There are a whole lot of ways that something can upset the ownership of a small business, and I really think this book covers just about everything. It also gives you a CD with forms you tailor to your situation and print out, as well as a tear-out form as an appendix. It can't get much easier.
This book is thorough, and covers both voluntary and involuntary transfer of ownership. For example, not only does it discuss how a buy-out agreement may cover the buy-out of an owner disabled by sickness or accident, it discusses the importance of defining "disability". How about if an owner loses a license needed for operations? What if an owner goes into personal bankruptcy (for circumstances not connected to the company)? A divorce, where the "leaving" spouse is awarded part of the corporate stock in the settlement is not uncommon, because the company stock may be one of the biggest assets of the owner getting divorced.
In each of these circumstances, if the stock certificates do not have notations indicating that they are subject to the shareholder's buy-out agreement, the remaining shareholders may be subject to a convoluted and expensive mess. A fair buy-out is just as important to the departing owner. For example, if you are disabled and need the cash now to pay medical bills, a buy-out agreement could help insure that you don't have to settle for a fire-sale price on your stock.
The authors give you a good run-down on possible tax issues, but if your situation or goals are complicated, they recommend you take your form to a tax advisor before finalizing.
The chapter on Structuring Buyouts notes that if the corporation or LLC is buying back the stock of a departing owner(instead of the other owners personally buying the departing owner's stock), the buy-out needs to keep in mind the state's rules on financial solvency. That is, after the buyout, the company must still have a financial statement that meets state requirements. The state may require, for example, that a corporation have total assets equal to 150% of total liabilities. If not carefully structured, a buy-out could result in significantly reduced assets (cash paid to departing owner) or significantly higher liabilities (a new note payable to the prior owner) that would keep the corporation from meeting the solvency requirement.
I will add that even if the remaining owners are purchasing the stock personally, they need to pay attention to state requirements if the remaining owners need to borrow from the corporation to pay the departing owner, or if the remaining owners need to take unusally high salaries or withdrawals to pay the departing owner.
Not mentioned in the book is the additional possible solvency requirements of a financial institution or bonding company. I worked as a surety bond underwriter for 28 years. Most of our accounts were contractors, but other types of companies also require bonds. I saw instances where the kids carrying on the company wanted to buy out their retiring father, but doing so raised the corporate debt so much that it was more difficult for the construction company to qualify for the same bonding limits it had before the buy-out.
In the same vein, many companies have a bank line, a short-term lending facility for cash flow purposes, generally for a term of not more than one year. It is common for a bank to add solvency conditions to a bank line, such as a maximum debt to worth ratio. If the corporation's debt ratio goes too high (because assets are lower or debt is higher or net worth is lowered because the corporation buys back stock), the bank can declare the loan in default even if payments have always been made appropriately.