HA...only on TV. In real life, an informant is anyone stupid or desperate enough to flip on the guy on step up the food chain. The informant makes the choice of whether to save himself and endanger his family or face full legal punishment for what ever the alleged crime.
LE, quite frankly, cares about their investigation. Norcotics handles the drugs, let patrol and the victim advocacy unit handle the informants safety.
In the end, LE doesn't make the choice, so they aren't in charge of the potential consequences.
That's just the way it works.