It will be kept going for a few years for primarily political reasons, allowed to wither on the vine, then will be quietly consigned to the aeronautical dustbin of history.
Having worked closely on the evaluation of the CS300 and flown in it many times, I think it will be a great success - not on the scale of the A320 or 737 families perhaps but certainly in comparison to E Jets and even the CRJ series. Airbus concluded that the economics of the aircraft are genuinely superior to the A319neo and that the seat/sector cost was even within a few percentage points of the A320neo. And wait until you fly in it - seat width, window size and noise levels make you realise just how 20th century the A320 and, particularly, the 737 are. To get into such a programme for free and knowing that they can take up to 50% cost out of supplied equipment while adding sales to jack up the production rate - thus further reducing cost - was a no-brainer. Flight deck commonality would have been great but, in the overall scheme of things, not that important.