what i think will happen is that when jagex realease their first version of mechscape or whatever their next mmorpg is most developers and other parts of jagexteam will move over to the new mmorpg. runescape will lose quite a few members, worlds will be closed down, less frequent updating etc etc.
who knows when they decide to release a new mmorpg. im guessing when runescape gets a bit out of hand (too much to control?), too expensive to keep running compared to members. they will eventually need to release something new.
blupig: wouldnt releasing updated graphics be a bit too much? i mean it will take them years to move over their existing game, instead they will work on something new and do stuff they could never do on runescape (no idea what, but runescape has too many limitations).