So I just installed the old Halo Wars 2 Open Beta on my xbox one aaaaand it’s still alive and kicking. I mean, I can’t get any matchmaking going because I guess I am the only one, but I suppose you could in theory play the game in deathmatch if others do the same? =)
There was a thread the other day that mentioned this. I searched and couldn’t find a game as well. Servers are most likely still down even though it lets you search for a game . 
At least halo wars DE is out tonight at midnight. Let’s just see how long it takes to receive the code from Microsoft lol =)
While the game may boot up, the beta finished quite a while back. The next beta for Halo Wars 2 will be in the new year