"Come away from the place they're currently at" or something like this. There has to be a prefix to make it perfective, and no other prefix could really work here.
- Bejönnek a városba -- that's often used, but mostly when somebody goes from the outskirts to the city centre, and never when going from a city to another one.
- Megjönnek a városba -- megjön can mean "to arrive", but it's awkward if it's followed by a location.
"Eljön" is used quite often. It's simply the opposite of "elmegy" depending on if you "come" or "go".
- Holnap elmegyek futni. -- I'll go running tomorrow.
- Eljössz velem holnap futni? -- Will you come running with me tomorrow?
- Igen, elmegyek veled. -- Yes, I will go with you.
So that el/away doesn't have to be translated all the time.
Well, if I am not mistaken, even English uses the phrase "I came away with the impression....". So, that's for the case when it is coming away from a source.
And when it is about a destination, like it is implied here, it acts as an indicator of a completed action. That is, the emphasis is on the result: them being here/there. Don't think of it as a direction. Think of it as a destination thing. That's why it is "perfective", as Shamarth says.
Here, it is not about coming from somewhere, hanem coming to somewhere, and ending up there.
So, the question really is: Are they going to be there?
Translating "el" as "away" could be very misleading sometimes. It is used in so many other situations that have absolutely nothing to do with any kind of (directional) movement. Instead, it indicates that "it will be done".
These things have been discussed in detail before. Who knows how to find them...