Sorry about the loss of your horse. 
See below for info regarding reporting a death.
16. DEATH REPORTS
The death of a registered Thoroughbred, or foal for which registration is pending, should be reported to The Jockey Club Registry Office within 30 days after the death by submitting a completed Report of Deaths form, or through Interactive RegistrationTM at registry.jockeyclub.com, and returning the Certificate of Foal Registration, if issued.
As a gelding, if he was through with his racing career and off the track I don’t think that it would really be necessary to report his death to TJC.