But I do agree with you that if the merger happens, some of the associates might very well be in jeopardy of losing their jobs. Let's take a look at some scenarios:
You have indicated that you would not necessarily be a viable candidate for the big firm if you were to apply to that firm directly. I am going to assume that you do not have the "right" school and/or grades that are normally required by this firm. Unless you are a star associate or work in a very unique and understaffed practice group, you might very well be one of the associates who are not included in the merged firm.
Here's another scenario: You are working for a partner who does not have any of his or her own business. The larger firm has a number of partners in this same department and they have less than significant books of business themselves. More than likely the new firm will "cherry pick." This means that they will select only certain partners or departments to be a part of the deal. If your partner is not included in the deal, you can count on the fact that you will be left out in the cold as well.
A third scenario: There are always a handful of partners who do not want to be a part of a merger. They will quietly go out on the market and look for a new opportunity before the merger is finalized. Even if the partner you report to thinks that you are the greatest associate on earth, it will be up to his or her new firm to decide whether or not they want to bring you on board with the partner. This goes to the question you asked about loyalty. Your partner may want to take you along, but if the new firm says no, he or she is not going to pass up on a great opportunity just to protect you.
Is there a partner with whom you are particularly close? If so, it might be time for a heart-to-heart conversation with him or her. This partner is unlikely to disclose confidential information to you regarding the potential merger; that would violate a partner's fiduciary responsibility to the firm. However, you might be able to figure out whether or not you are going to be a part of a potential merger and if this partner is willing to fight for your inclusion. If you don't feel that you are going to be a part of this partner's merged group, you really need to pay attention to your instincts and dust off your resume!
The best suggestion I can make is that you need to decide if you want to be an associate at the merged firm, should the union occur. If so, I think you should take the chance that you will be asked to be a part of the merger. If the potential new firm is not where you want to practice, then you should be out there looking for a new place to work. Even if this merger does not go through, your firm will become known as one that is open to exploring merger opportunities and, no doubt, other law firms will make efforts to merge your firm into theirs.
If you are well-liked and respected by your current firm, have been receiving good reviews, and are happy, then I would advise you to stay put until you know for certain that things are about to change. I hope this advice helps.
Summary: I'm an associate at a mid-sized firm. Rumor has it we are about to merge with a BIG national firm. Should the associates be worried?