Once glandular tissue forms behind the male nipple, can it go away without surgery?

Excess glandular breast tissue in males, regardless of age is called gynecomastia. In usually first appears during puberty. if it does not go away within two years it will usually remain for life. Surgery is really the only treatment.

Yes, breast glandular tissue "can go away" without surgical intervention;  this is most commonly seen in pubertal gynecomastia. Once gynecomastia has been present for longer than a year, it is unlikely to spontaneously resolve.   In most cases, gynecomastia is treated with resection of the excess breast tissue; peripheral chest liposuction surgery may also be helpful. I hope this, and the attached link dedicated to gynecomastia surgery concerns, helps. Best wishes.