For many different reasons, your Massachusetts personal injury lawyer may terminate the lawyer/client relationship with you. The lawyer can generally do this at any time unless the case is in litigation. If the case is in litigation, then the lawyer will need the permission of the court, and the court will only allow the lawyer to withdraw at that point if it is convinced your legal interests will not be prejudiced.
Assuming your case is not in litigation, you may receive a letter from your Massachusetts personal injury lawyer telling you that he is referring your injury case to another lawyer. That is perfectly fine. But, the highest court in Massachusetts, the Supreme Judicial Court, announced last fall that the client must be informed about the referral, and must accordingly consent to a fee sharing arrangement between the first lawyer and the second lawyer. Therefore, if your existing lawyer refers your case to another lawyer, and he expects to receive a referral fee, he will need to have you sign something that says that you consent to the fee sharing arrangement.