It is true that there is existing conflicts between the street gangs and the government. However, this instability is happening in the city of San Salvador, which you won’t visit during the retreat Salty Souls. The airport, even if named like the capital, isn’t actually located in the city, so you won’t find yourself in a dangerous situation there either. Moreover, the tourists are not targeted by the conflict. The Salty Villa is located in a quiet beach town (El Tunco), and is fully gated with a 24h/7 guardian.
We personally never felt unsafe in El Salvador, so you should not be worrying. 🙂