It is worth noting that Bristol was already out of Drills by early 2020, over two years before the Gardens' closure, with the last male having left for Barcelona Zoo (per ZTL), and with the other three animals having already passed away, so as lovely as it would have been to see them at Wild Place / Bristol Zoo Project, whether that is in addition to or as a replacement for the Geladas, it was never really an option. .
The other three Drills aren't dead, they ( a female and her two daughters I believe they were) were sent to Fota Wildlife Park in Ireland. Couldn't understand why they broke up this group after the fanfare of getting them just a few years previously. They may have needed a new unrelated male but that is always possible. But did Bristol not have any idea they were going to need to add to the stock at Wild Place even back then? I don't know the answer to that one...