1) No Guarantee of Success: Well written and properly plead mandamus lawsuits have an outstanding track record of success in terms of getting a decision. However, it’s important to note that nothing is ever guaranteed when it comes to legal outcomes. Anyone who tells you otherwise is misleading you.
2) Compel Action, Not Outcome: A mandamus lawsuit can compel a government agency to take action on an immigration case, but it cannot dictate the outcome of that action. For instance, if an immigration application has been pending for an unreasonable length of time, a mandamus action can force USCIS to make a decision, but it cannot mandate that USCIS approve the application. That said, retaliation is basically unheard of. A strong case should get approved, just faster. On the flip side, the same is true for a weak case. They will get denied, just quicker.