It’s about what dad can gain from being told. Covering up a mistake like this is condescending and any confidence that lets him keep is false. Part of being up to the job is a realistic idea of your capabilities and the ability to receive feedback. If dad’s still a peer and a real part of the team, he needs (and gets) to know. Hiding accidents like this to maintain a more comfortable reality is how you handle a patient during end of life care, not someone who’s still living and working in the world we share.

Conversely… at some point our capabilities dwindle, no one gets to participate in our shared reality forever. If your father’s at a point where you need to shelter and protect him there’s nothing wrong with that, but it’s quite a heavy responsibility to assume and not necessarily going to be easy or fun for either of you. Very similar commitment to raising a child, but keeps getting harder until they die instead of easier as they grow. It’s heavy stuff and no one here can answer this for you op. The way you frame this makes you seem like an intelligent and caring person, you’ve got this. Good luck out there.