"[W]hat are your responsibilities [as a TPA who has agreed to take on plan administrator responsibilities for a retirement plan covered by ERISA] if you become aware that the plan sponsor or trustee is proposing to take or has taken actions that harm the plan? ... [M]ere resignation is not sufficient if you are a fiduciary. In fact, only resigning may make you liable for the wrong-doing that you are attempting to forestall.... Perhaps the first thing you should do is put your client on notice that your interests may end up being adverse to your client's.... Second, you should be prepared to 'ring the bell' when there is a breach of duty by another fiduciary."