First, let me state that I have no info whatsoever in regard to Casey's future retirement plans, if any. With that said ...
Blax, you're entirely correct that there are very few new girls coming onto the scene with truly large implants to continue the huge boobs tradition. At the same time, some huge boob girls from the mid-90s heyday already have or will continue to "retire". There are several reasons for this.
#1 - today's very high cost of obtaining very large implants , due in large part to stricter FDA rules
#2 - today's comparatively low income potential from club feature fees, magazine modeling fees, single girl websites, and other traditional income sources
#3 - today's reliance on XXX and "one on one private sessions" with fans as essentially the only remaining major sources of income for huge boob girls
These points and others have been discussed at lengths in various threads here at BEA.
Of the new huge implant girls that have entered the scene and who frequent the BEA, i.e. Christine, Vixen and Kiesha, it has taken Christine over a year of "exposure" in XXX videos to finally draw the serious attention of cable TV and magazines. Even so, she still has to work a "day job" and is not yet able to afford bigger implants. Vixen has just recently been able to pay back the money she borrowed to get her latest implants, and because of surgical complications isn't yet able to seriously pursue a big boobs career. Keisha was hurt badly from a financial standpoint when her website's credit card processor went bankrupt, leaving her "holding the bag" to pay her website's bandwidth bills for members but receiving no membership payments. Today's very poor financial scenario means that girls will no longer invest in huge implants for business reasons - meaning that Christine, Vixen and Keisha are even more special since they got huge implants primarily because they love having huge boobs! In contrast, today's trend of magazines using "natural" girls is probably due to a combination of the lack of new girls with huge implants, combined with the fact that "natural" girls have nothing invested in their chests such that they have lower earnings expectations.
Back to the original subject of Casey retiring, again I have no knowledge whatsoever in this regard. However, it's not difficult to point out that Casey has chosen not to participate in the XXX video arena, and that Casey has also chosen not to participate in the "one on one private sessions" area either. This would tend to indicate that Casey is affected by todays' poor economy to a greater degree than other girls who have a large XXX video presence and/or who regularly do "one on one private sessions", such that there would probably be no strong financial incentive today for her to continue doing what's she's doing from a purely business standpoint.