Riot deleting dominion shows an inherent flaw in how they handle their game client.
No LAN (local area network) support for their game.
If we had LAN support, someone could just archive/snapshot the current patch, and anyone who actually likes to play dominion could get people together and play it without using Riot's servers.
Sadly now it will just die forever, because in the 6 years League has been around, Riot hasn't released LAN support outside of the LCS.