I read a lot of novels, and in novels they are always changing the dealer when they think a player may be "counting the cards" etc...
Der Fish
In "real life" casinos in Atlantic City, the dealers rotate on a set schedule. At the craps table they rotate 20 minutes at each position, so one hour at a time, then they have a 20 minute break to eat/restroom/check e-mail/whatever. Other games they rotate tables, 20 minutes each, also working one hour on, then 20 minutes off. If a dealer feels ill, they can request to be "tapped out" [replaced], they don't pull dealers because someone is winning. The "eye in the sky" cameras watch everything.