I've been thinking about how the 4e verson of DS will be based on the original boxed set and it has me wondering what parts of the setting will change, like the map. If the new setting shows just the original Tyr Region, then no worries, but what if they want to show more of Athas, can they ignore the revised edition map? Sure they can, but how does that 'feel' to the player-base? As a game designer, can you 'wish away' parts of the setting? Can you say that the City-State of Kurn never existed?
They can retcon the timeline to say that the Prism Pentad was a possible outcome, but can say that New Giustenal doesn't exist? Especially since Bill Slavicsek helped design it.
I'm dying to know more about the setting, come on sneak peeks!
To answer the title of your post, I would say that yes you can retcon a map. Even though I wouldn't exactly call what happened to FR as 'retcon' --since, technically, the story was moved forward and not retconned-- I'd still point to that as an example.
To answer the content of your post... I really have no idea what to expect from 4E Dark Sun, but it wouldn't surprise me to see Dark Sun go through some changes so as to fit the 'core' races and ideals of 4E into the setting.
. . . but what if they want to show more of Athas, can they ignore the revised edition map?
I hope so. I want map that matches what was described of the world beyond the Tyr region before the revised boxed set threw it away and invented something else.
Before the revised set, the Silt Sea was surrounded by the Tablelands, all of which was "ringed" by the Ringing Mountains. I had imagined some continental-sized crater. (Would have been cool!) If the 4e DS reverts to this, I'll be a happy gladiator.
I'm trying to remember if they have ever redone a map of a setting before... I seem to remember they have but I can't remember. I've never followed any of the other settings, I've only used Greyhawk, Dark Sun, and my Homebrew. Did they re-draw Krynn?
Just for clarity, I have no qualms with them destroying the Mind Lords of the Lost Sea, and actually hope they do, I'm just wondering if there is an historical precedent for such things.
The northern map doesn't forbid that design of the Ring Mountains encompassing the Tablelands, as nobody canon has ever shown the eastern half of that equation. If the old map only shows the middle western edge then the expanded map show what lies north of that area outside of the crater remnants.
The Ringing Mountains, IIRC, were never a complete ring. As described in the WJ, there were two chains of mountains, running more or less in parallel. While the DS2 map makes it slightly less likely, there is nothing that truly rules out the mountains as described in the WJ.
I'm at work, or I'd actually verify ...
I'll quote, we can all judge. 
From the WJ, page 4,
"The Tablelands are encircled by various ranges of the Ringing Mountains. These ranges all run north and south. To the east and west of the Sea of Silt, the mountains form solid walls separating the tablelands from the unknown regions beyond. To the north and south of the dusty sea, they form a series of parallel ribs. The deep valleys between the ridges lead away from central Athas like a series of long (and hazardous) corridors)."
I don't think we can honestly say that the regions to the north and south don't have anything like a series of parallel ribs with long and deep valleys. There is certainly no "encircling". To me, it takes a seriously . . . uh, open minded . . . reading of the quote above to fit that onto the DS 2 map.
It can also have to do with scale, you could still add mountains to the north of the Burning Plains, and south of the Dead Lands.
Then, Eric, all they need to do is rename the current mountain chain the Western Ringing Mountains.
The community has been missing your involvement, Eric. Glad to read your posts again! ;D
The community has been missing your involvement, Eric. Glad to read your posts again! ;D
I won't lie, the 4e DS announcement got my attention back.
You can do anything you want with your Dark Sun world.
I was playing before the revised edition came out. In my world, instead of Thri-Kreen, there was a sea that provided the moisture that feeds the Forest Ridge.
And it's the Rining Mountains, not because they ring the Tyr Region, but that a ringing sound is heard when in them from the wind.