IMO discord is not great. I might be in the minority but everything these days offers a discord because it's simple. I'm not a fan of it and would prefer IRC. Part of that reason is discord is just spying equipment dressed up with a nice UI.
I couldn't imagine using discord for a company. Slack actually provides some value outside of just chat that makes it legitimately nicer than the mid 00's solution of AOL messenger (or MSN) that companies used to use. I don't think self hosting a chat of similar value would be much cheaper if you did it properly. 1,000 users will require plenty of servers and failover, plenty of storage for messages (even if you cut it off at 90 days), etc. A lot of people use slack as an ad-hoc note storing service with search so go ahead and add even more hardware. On AWS this would get prohibitively expensive quickly. Honestly I could do without 90% of the features and would be very happy if I could just run IRC in my terminal for work. Unfortunately IRC is non-trivial to get a normal person started on.
I couldn't imagine using discord for a company. Slack actually provides some value outside of just chat that makes it legitimately nicer than the mid 00's solution of AOL messenger (or MSN) that companies used to use. I don't think self hosting a chat of similar value would be much cheaper if you did it properly. 1,000 users will require plenty of servers and failover, plenty of storage for messages (even if you cut it off at 90 days), etc. A lot of people use slack as an ad-hoc note storing service with search so go ahead and add even more hardware. On AWS this would get prohibitively expensive quickly. Honestly I could do without 90% of the features and would be very happy if I could just run IRC in my terminal for work. Unfortunately IRC is non-trivial to get a normal person started on.