Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am sorry to know about this sad event. I can understand your concern. Many times, depending on the person's sensitivity, they could be more or less vulnerable to be impacted by scenarios like this, which use to be traumatic, and develop anxiety or depressive disorders.
Right now, you have been wise asking him to share with you what happened and how he feels. It is a positive sign he seems fine, what does not deny the possibility of this affecting him in the near future. How to know and what to do? Just be patient and keep observing him, his mood, functioning, rest at night, daily habits and relationships. If everything in those areas remain fine, then no reason for you to worry about it.
In case you observe any significant negative change then you would address it with him and consider individual counseling in order for him to get adequate support, process the traumatic experience and move on.
Death is part a natural part of life, and mainly because of the tenor of beliefs people are raised with and reinforce with time, issues with scenarios like this or similar arise. This could be a very useful chance you got to work on improving coping skills and insight on this matter, for your son to mature and become even more assertive so to better cope with any situation related to death.
Please do not push yourself worrying about it but better focus your energy and attention on being proactive and supportive for you and your son to process this event the best possible way. Feel free to contact me for any further clarification or support. Thanks.