Make two triggers covering the area of the town.
First one (slightly smaller)
Activation box: East present
countdown: 60 60 60
On activation: eastHere=true
Second one (area you have now)
Activation box: East not present
Type: End#1
Condition: this and eastHere
What will happen is that when east enter the area the variable eastHere will be set to true. (There is a delay of 60 seconds so that if the first loon to cross into the trigger area gets killed straight away it doesn't trigger the ending) The east not present trigger can only fire after the first trigger has fired.
The question made perfect sense .... I hope the answer does too.