Naturally she will have a career as a Singer, but unlike Taeyeon that interestingly started her Solo debut a few weeks before TWICE debut, Taeyeon was able to do it because SNSD were all but headed toward hiatus.
TWICE can still do American Stadiums and Tokyo Dome Concerts so for Division 3, it will still be a balancing Act, but considering how many Comebacks TWICE did in 2017, 4 Korean Comebacks and a Japanese debut, I'm sure that TWICE, Nayeon, JiHyo and Chaeyoung will be making Solos in the same year.
Nayeon and JiHyo have always been favored by JYPE, I can see them still being there in 2028 when JYPE will debut Nayeon's grandkids :P