I am explanting. Is it important to explant en bloc and does the muscle have to be sewn back?

Thank you for the question. Don't be surprised if you receive a variety of differing responses.
Generally speaking (in my opinion), unless the breast implant capsules have thickened (and/or are otherwise symptomatic), are associated with the ruptured silicone gel breast implants, or if the patient has concerns about "medical conditions" related to the breast implants, capsulectomy is not universally necessary. For these patients, en bloc removal of breast implants is a good procedure.
On the contrary, capsulectomy can expose patients to additional risks, such as bleeding, size loss, contour irregularities and other serious complications. In other words, any maneuver performed during surgery exposes patients to additional risk (morbidity). For example, attempting to remove very thin capsule densely adherent to the patient's rib cage may expose the patient to significant bleeding and/or entrance into the thoracic cavity.
 
I hope this helps. Best wishes.
 

Patients seeking implant removal have many options now.  En bloc does ensure that the implant and the surrounding capsule are removed in one piece. I always recommend muscle repair in situations that the implant was originally placed under the muscle.  Learn more about en bloc in the video link to make a more informed decision.  Good luck.