Unique challenges face firms with 1, 2 or even 3 partners. The first is that you are the firm. Even in a 3-partner firm, unless your partner(s) have extraordinary excess capacity, there is typically little or no back-up on a partner level in the event you are unable to provide time or service to your clients.
Another unique challenge is reading your client's mind because if you are over the age of 55 your clients are beginning to ask: "I wonder how long my CPA is going to do this?" If that question has been posed to you, know you have already lost referrals and opportunities. For every one person that has asked that question, 20 more are thinking it.
In addition, your clients are traditionally "partner" loyal, not "brand" loyal. The clients of a Big Four firm stay with the firm regardless of partner rotation because they are brand loyal. The clients of your firm have a much more personal relationship with you, which exacerbates the lead time needed to implement a proper transition.
You can control succession (or the selling or your practice) if you understand your options and have the information to make informed decisions.