Before the adventure begins, it is wise to draft up a document stating what will happen if the venture fails. Think of it as a pre-nup for a business. It's a bit of doom and gloom while you are in the honeymoon phase of the business, but it's a lot harder to determine what to do when all parties are upset and losing money.
Examples are:

• If there is capital involved, will it be sold?
• How will it any remaining funds be split?
• Does one partner have first right of refusal?
• If one partner wants to get out, what steps will be taken?
  • Is there a penalty for exiting the company before a given time?
    ...