Emily Coutts (Detmer) and Oyin Oladego (Owo) are never listed with the main cast characters. They and others like Patrick Kwok-Choon (Gen Rhys) are credited in the ‘also starring’ list in the post credits not in the main titles.
No reason not to believe Emily won’t be back. Oyin was in production as the lead in an independent feature last year so there may have been a scheduling issue as there was for Ronnie Rowe Jr (Bryce) when he was in production for his lead role in BET+ Series ‘The Porter’ during production of Discovery season 4.
Most of these Canadian actors filling in the bridge crew work on other Canadian projects which seem to be more crucial for advancing their careers even if working on Discovery was a regular income.
Clearly, the ability to be outside in appropriate clothing for activities isn’t being mandated. This is where a temperate climate enables ridiculous practices to persist.
All I can think about when I see this image is how in Ontario, the responsible provincial ministry requires all schools and ‘day nurseries’ (read day and after school care) to put the kids out in the yards twice a day unless the weather conditions are severe (Less than -20 or more than +30 Celsius.).
Parents are responsible to send their kids with suitable clothing for the cold. One rarely sees little girls in skirts in schools unless they are wearing tunic dresses over leggings.
In an earlier era, pre 1970s, when skirts were mandatory for girls, that meant switching to pants or snow pants from the skirts 3 times a day to go outside in winter (two breaks and leaving end of day).