1. Config Values
class CfgWeapons {
    class MyWeapon {
         ace_hitreactions_undroppable = 1;  // Prevents weapon from being dropped
    };
};
2. Mission Variables
2.1 Safe pickup distance for AI
Allows 3rd party mods to set the distance between AI and the nearest hostile that is considered safe to go pickup a dropped weapon.
ace_hitreactions_safePickupDistance = 10; // default is 8