A friend of mine drowned a few years back while drinking. The guys he was with swam to shore after the boat overtuned and said he was just gone.
A few months later I talked to the cop who recovered the body and he said that my friend likely slid beneath the water and never came back up or struggled.
If the person goes in and gasps for air underwater he probably wont come back up again.
Drinking plays a big part in a lot of drownings. A few years back working EMS I had the displeasure of responding to a drowning call. In spite of responding within three minutes of the call we spent an hour trying to find the victim because his buddies were too intoxicated to tell us where he went into the water. Had they been coherent, the water was cold enough that we might have located him in time for a resuscitation.