As Statyk said, you will need to use global variables. Create a file called "global.hps" and put it in your maps folder. Then write this in the file:
void OnGameStart()
{
    SetGlobalVarInt("EventHappened", 0);
} 
 (you can name the variable anything you want)
Then once the event happens in the other map and you want to activate the script area, write 
AddGlobalVarInt("EventHappened", 1);
In the script for the map with the script area, write this (make sure you write it in the OnEnter function):
void OnEnter()
{
    if(GetGlobalVarInt("EventHappened") == 1) {
        SetEntityActive("ScriptAreaNameHere", true);
    }
}