That's an odd way of phrasing the plot, as that makes the film sound more like a prequel than a sequel. The film is about Woody and Buzz finding Bo Peep, since she was absent in Toy Story 3. That doesn't sound unnecessary to me.
Woody and Buzz go out to find Bo Peep and bring her back.
I think the idea sounds great, and I think it has a lot of potential. I enjoyed Toy Story of Terror! and Toy Story That Time Forgot and the other Toy Story shorts, and I'm excited to see these characters again.