Probably we are. If we leave the EU we lose voting membership of EASA. If we leave EFTA/EEA we lose non-voting EASA membership. If we become a "Third Country" we can probably cobble together something like the EASA/Turkish arrangement whereby Turkey is a high fee, non-voting supplicant who's DGCA is permanently in thrall to EASA. Given that it will take years to resurrect a half way efficient UK CAA to act as an independent aviation safety system in the event of leaving EASA, we'll be in Armaggedon territory fairly quickly thereafter, descending from membership of world aerospace leadership with hugely significant collective national experience, skill, innovation, manufacturing capability and technical excellence to a dark world of UK job losses, skill migration, airline closure and manufacturing collapse.
This looks like the frightening talk which did not persuade remain result in the Referendum. I cannot see Mr Rees Mogg sitting back while we become a "vassal state" though.