There’s no way to know when/if he will wake up at the beginning. Usually we try to use the least sedation possible to keep the patient comfortable (based on non-verbal signs) and in synch with the ventilator. If that can be achieved with a low to medium dose, then the patient can wake up once their brain recovers enough. If he’s condition had been such that he needed deeper sedation, then sedation would be lightened when those other problems improved.
The brain isn’t going to benefit from the sedatives, especially at high doses. The more time a patient spends on high-dose sedation, the more confused they get. Sedation is dosed at “just enough to get the job done”. The nurses have protocols for adjusting sedation doses based on what’s going on. If you every hear of someone being in a medically-induced coma, think of it as a necessary evil to help facilitate other therapies to support one or more failing organ systems, rather than a therapy in and of itself. There are rare instances when the sedation is the therapy (e.g. continuous seizures that we can’t break), but usually it’s there to facilitate other therapies.