Davies was out of action for nearly nine months, after having a plate inserted and enduring muscle wastage during the rehabilitation period.
Former All Black Gatland booked his flight home this week, just as he announced his initial Welsh World Cup squad.
Highlanders assistant Mark Hammett said Bryn Gatland had broken at least two metatarsals, damaged ligaments and displaced something else.
The horror injury has also robbed the Gatlands of a footy father and son reunion.
Outgoing Welsh coach Gatland is tipped to guide the Barbarians against Wales late this year. Bryn Gatland was in line to play for that team, giving his father the opportunity to coach him in a top side for the first time.
Gatland has also become favourite to coach the British and Irish Lions in South Africa in 2021, which would be his third successive tour with them.
In 2012, Gatland snr suffered two broken legs after falling from a ladder at his Waihi Beach bach.