Non-FT violation during FT

[Rob1968]

So, has this, or is this likely to ever occur?

Certainly, if the player approaches his/her bench to take a drink, or to use a towel, and steps off the playing surface, it's a non-issue.
And if the official sees a player leave the gym, without being subbed, the next thing to do is to approach the coach - maybe the player is ill, or about to vomit, etc.
There are so many circumstances during a game in which the penalty is available, but we explore the specifics of the situation first.