I think FFXIV is better be seen as a new Final Fantasy game with better technology rather than a simple successor to FFXI. But technology is not everything, the key is still the game play.
They say it many times that FFXI will be in service as long as there are enough people playing. No one is losing any toons .... yet. Although I am more worried about getting new players to FFXI after FFXIV coming out; it will all depends on how good is FFXIV is.
Amanada (Cerberus-Retired) (aka MaiNoKen/Steven)
-- Thank you for the fun times in Vana'diel
Art for the sake of art itself is an idle sentence.
Art for the sake of truth, for the sake of what is
beautiful and good — that is the creed I seek.
- George Sand
A designer knows he has achieved perfection,
not when there is nothing left to add,
but when there is nothing left to take away.
- Antoine de Saint-Exupéry