If I were in your shoes I would go for the full IO, better to be rid of the thing than to chance allowing even the possibility of malignancy any toehold. Sounds like the remaining testicle would become problematic anyway if it becomes atrophied. Also, you can bank sperm prior to the surgery to ensure there is viable sperm later on when you want to have kids.
03/16/2012 Ultrasound Diagnosis TC (Tumor 5.5 cm)
03/22/2012 Right I/O Pre-IO markers normal
03/28/2012 Pathology Classic pure Seminoma, pT1/N?/M0/S0
04/05/2012 CT Scan--Clear? (single 1.2 cm node External iliac)
05/03/2012 PET Scan CLEAR. All markers Normal.
05/04/2012 1 X CARBOPLATIN INFUSION (Chemo Lite)
09/02/2012 CT All Clear! (1 cm External Illiac Node)
04/04/2013 CT All Clear!