will ONYXIA progress to Cataclysm?

will ONYXIA progress to Cataclysm? or the wotlk is the final expansion?

Onyxia will stop at the WotLK expansion. Once all the content has been made available, Onyxia will be merged with Icecrown. Your characters should transfer over to Icecrown automatically when that happens.

See https://forum.warmane.com/showthread.php?t=484296 for a bit more information on the transfer to Icecrown.