but have not returned since

[Maybo]

Around 2,900 missing persons reports have been filed in connection with Saturday night's crush, the Hannam-dong Community Service Center has told the BBC.
Families of those who attended the Halloween event but have not returned since have been registering queries with the centre, which is located in the area where the accident happened.
(Seoul Halloween crush kills 151, injures 82 by BBC)

I have some problems understanding "since".
Does the above news mean "...... but have not returned since (Saturday night's Halloween event) have been registering ......"
Am I right?

 

[5jj]

Yes.

 

[Maybo]

Do people end a sentence with “since”?

For example:
They attended an event last night but they have not returned since.

 

[5jj]

They can.

It's not very natural in your sentence. 'Yet' would be more likely.

 

[emsr2d2]

The use of "returned" is what makes "yet" more natural than "since" in that sentence.

a. I last saw Helen when she left the house on Friday night. She hasn't returned yet.
b. I last saw Helen when she left the house on Friday night. I haven't seen her since.