Your 10 M and 1M stats are close but since they got bought for over 750 million by FB’s gaming arm, Zynga, I don’t think they are just going to milk HOTM. They already have new event heroes for each event. They added Muggy to Atlantis. The downloads don’t matter, but 1M active daily users does. Even AAA games on consoles would love numbers like that. Call of Duty which is about as big as it gets, has several million players with a few million actives. A mobile game with 1M active dailies is insane. That is a hit. Not angry bird or candy crush level but for an rpg it is great. With ad money and in game sales they don’t need to just depend on the HOTM.
Also, they released a second game called Puzzle Combat which is another match 3 game that looks and plays just like EnP but the heroes are military types with guns and the tiles change to bullets and missiles instead of troops. It is only at v 0.9 and not available in the US yet they have tons of downloads and a forum with active users. Why would they not want to make a S3? It will renew the older player interest(including mine as I beat everything on S2) but I still play to level my heroes. I know that won’t last forever but hopefully S3 comes out soon and they give global access to Puzzle Combat so I can play that and chase those 5* LOL.
Here is a site with some mobile game stats for those that want to dig around. It is an enormous business. Why quit with only HOTM when a new season would get people to keep playing and with more heroes they would spend more money.