Given that League of Legends, Dota 2, and Blizzard's own Heroes of the Storm all share virtually the same map today, and are not engaged in any IP battles over it, I don't see any reason to believe Blizzard owning the original IP of the DOTA mod would have made any difference in terms of blocking the map design from being reused in other games. If anyone could have owned this map design, either Riot or Valve would have already sought to block the others from using it.