I have always been a Taylor advocate, so I believe Taylor, Thomas and Steffy should all return and be reunited with Ridge. They should start their own couture fashion house and go head to head with Forrester. Caroline would be a casualty in this which would be unfortunate as I really like her character.
However, I love Steffy (the character and the actress) and would love to see her return for a longer stint. She engineered the company take-over from Dollar Bill in the first instance, so I would love to see her wrest the company from Rick and retain complete control. I would put Rick in shipping, keep Maya as a model but upgrade Nicole to lead model. Ridge and Caroline could continue co-designing much to Steffy's disapproval of Caroline dating her father. The animosity between Steffy and Caroline would be fantastic. As would the animosity between Steffy and Rick. And best of all, as Brooke would have no say on anything regarding the business, Steffy could send Brooke but into the lab to discover an updated version of BeLief - she needs to earn her keep in some way. I could go on and on.