Thank you for expanding. Sure you can prepay up to a certain extent. Eventually your domain will be available to others for purchase and therefore your accounts will become vulnerable. Maybe this isn’t an issue if in the worst situation you’re not around but if this could cause chaos for your friends and family I would suggest taking it into account.
Given that domain renewals can be purchased multiple years into the future, along with the fact that there are grace periods after expiration, it would take an awful lot of failure to lose a domain unintentionally. I've held my primary domain since 1997 multiple registrars and numerous hosting / colocation arrangements over the years. It sounds harder than it is if you haven't done it before.
