The possibility of a lot of (habitual - ?) alcohol has certainly crossed my mind. It could indeed have been a factor in his decision to accept the client, and in his drafting of that extraordinarily bad and amateurish filing such as he submitted last week.
But then again, he was probably only presented with details about the client and the “defendants” that painted a picture of a slam-dunk case. Remember that LK’s suit was filed before the criminal trial, so Nagel may have assumed - like LK - that the case would be a quick victory. He would lean on MB and SGF a little bit, the carrier of their liability policy would immediately offer a settlement, LK would get her win, and he could add another jewel to his crown of accolades.
It must have been a bit of a shock to him to have learned more about his client over the past few years.