Does sewn cartilage stick together and becomes one piece or how does it work?

Cartilage that is sewn together during rhinoplasty heals by a process known as fibrous non-union.  One piece of cartilage that is sewn next to or attached to another does not grow into the other piece but fibrous tissue develops between the two that keeps them together but it isn't as strong.
Changes can be seen after a rhinoplasty years after the original surgery depending on what was done at the time of the operation.  If you're considering a revision, I recommend in person consultation with a facial plastic surgeon comfortable with rhinoplasty.  Good luck!

You are doing the right thing by researching your potential revision. For revisions to be successful, careful analysis and surgical planning are essential. Cartilage grafts will not merge with native cartilage. Instead, grafts will typically scar onto the preexisting structures. Grafts are used in most rhinoplasties, but they can resorb or warp with time. Discuss the plan with your surgeon. Make sure you understand and feel comfortable with it. Good luck.