This is a common question, especially in the legal field. And it is a very important question. First, a client is not automatically portable simply because you brought them in or you are representing them.
There is no sure way to tell if a client will be portable. When a lawyer leaves a firm, in the United States at least, both the lawyer and the firm need to make it clear that the client has a right to choose whether to stay with the firm, go with the lawyer, or find a third attorney/firm to represent him.
There are ways to analyze whether the client will move with the lawyer to a new firm, but there are no guarantees. Some things to analyze:
1. Did the client come to the firm or the lawyer?
2. How did the client find the firm or the lawyer?
3. What is the client’s relationship with the lawyer like. Is the client happy with the lawyer?
4. Is the client really the lawyer’s client or the firm’s client.
5. Where is the lawyer going? Is it advantageous for the client to stay with the firm or go with the lawyer? In other words is there some benefit to staying with the firm?
6. Where is the case? Will the case be delayed depending on whether the client stays with the firm or goes with the lawyer?
7. Where is the new firm? Is the office location convenient to the client?
8. Is there something very unique about that lawyer? Is he famous for that area of practice? Seen as a top lawyer that cannot be replaced?
9. Or is there something unique about the firm? Is it famous for that area of practice, seen as a top firm, that cannot be replaced.
10. Why is the lawyer leaving the firm? Is the separation good or bad? If bad, who looks worse and will the client know.
Those are just a few of the questions to ask in making your analysis. Generally speaking, when a lawyer leaves a firm, a certain percentage of the clients will stay with the firm. How many depends on many variables.