To be honest, it is realistic for people to eventually discover this. One can't simply get away lying that they're this brilliant student from Harvard in a law firm full of Harvard graduates. Yes, the nail-biting excitement has diminished quite a bit because almost every relevant character knows about him now, but it's still hidden from the legal world at large. So the stakes are still high. And they're getting higher as more people are in the know because more the bearers, more the chances of a leakage.
They can weave an interesting story even now if they're creative enough. Eventually, every series moves away from it's initial storyline. Circumstances change whether in real life or in the world of fiction. The focus has already started shifting towards other stuff.
P.S. I don't know if they're thinking yet towards when or how to wrap up the series but I see a fitting conclusion as Mike getting a legitimate law degree and continuing his practice.