One company I worked for used to have an unofficial “ex-company” slack setup, where people would get invited to by others that have already left and were in there, it was kinda nice since you form bonds with people and suddenly they’re just gone. You might have not managed to connect with them in any other form.
But you login to “ex-company” slack workspace and here they are - everyone that went through the company. I mean lots of people would stop responding after a while, but there was enough time “buffer” to allow people to connect with other means.