Will leaving behind a small amount of glandular tissue after gynecomastia surgery become a complication?

The goal isn't to remove all of the breast tissue (since the nipple and areola are breast).  However, the majority of the tissue should be removed and this can ONLY be achived with surgical excision (not liposuction).  When the procedure is done properly it almost never "grows back".

The areola and nipple is breast tissue. Preservationist to structures by definition leaves behind some breast tissue. This is a normal way to treat gynecomastia.

A small amount of glandular tissue should always be left behind to prevent the sunken look. A completely flat chest is not the norm and fat tranfers are unreliable and may cause further deformity when some of the fat is re-absorbed. Good luck

Some breast tissue must be left behind to allow for vascularization to the nipple and areola.  If there is any further stimulation of breast  tissue then you can get a recurrence.  

Leaving a small amount of tissue under the areola will help minimize the risk of a crater deformity. Best of luck.

Leaving some tissue under the areola is the best way to avoid crator deformity of gynecomastia operation.  Fat grafts are unpredictable at best.  They are used to treat deformity.  However it is best to avoid this deformity by doing surgery properly in the first place.