Yes, your new cruise will go to the TA you booked the current cruise with. If you want something different then tell the booking agent on board .
Also, it has happened to us a few times that Celebrity didn't let our TA know of the new cruise and she had to go searching for it so KEEP ALL PAPERWORK!!!
(It's a pet peeve with me that Princess is able to not only keep everything straight but also all of my cruises , FCCs and other details are able to be viewed by me online. If Princess can do it then Celebrity ought to be able to figure it out.)