Vaginoplasty can result in fistula, stenosis, necrosis, prolapse and even death.
Male-to-female genital surgery (vaginoplasty) is associated with significant long-term complications: there is a 2% risk of fistula, 14% risk of stenosis (abnormal narrowing), 1% risk of necrosis (tissue death) and 4% risk of prolapse .
One systematic review  found an overall complication rate of 32.5%.
A Dutch study  of 55 (out of an original 70) adolescents treated with puberty blockers, cross sex hormones, and genital surgery, showed that among 22 male-to-female patients who underwent vaginoplasty, one adolescent died as a result of necrotizing fasciitis after the surgery.
 Manrique, O., Adabi, K., Martinez-Jorge, J., Ciudad, P., Nicoli, F. and Kiranantawat, K. (2018). Complications and Patient-Reported Outcomes in Male-to-Female Vaginoplasty—Where We Are Today. Annals of Plastic Surgery 80 (6): 684-691. [Link]
 Dreher, P.C., Edwards, D., Hager, S., Dennis, M., Belkoff, A., Mora, J., Tarry, S. & Rumer, K.L. (2018). Complications of the neovagina in male-to-female transgender surgery: A systematic review and meta-analysis with discussion of management. Clin Anat. 31 (2):191-199. [Link]
 de Vries, A., McGuire, T., Steensma, E., Wagenaar, T., Doreleijers, P. & Cohen-Kettenis, P. (2014). Young adult psychological outcome after puberty suppression and gender reassignment. [Link]