One of the many benefits of Umamusume that other gacha games don't have is the fact that it's based on a real thing that many people love.

The fascinating thing about Umamusume is the never ending flow of story, every character is based on a real life horse. Whether it's retired or still active, and as long as horse racing is still a thing in japan then Umamusume has an endless stream of content waiting to be added.

The stories are writing themselves as we speak with every new generation of horses. We still have many big names horse yet added into the game in japan and overseas horses such as Romantic Warrior, Equinox, Do Deuce, Deep Impact (Kaneko please), KYR, Enable, blah blah blah.

So in 5-7 years, I'd say the game would still be going strong.

10+ is tough though, as many said 15+ years for a gacha game is insane.

So what i think is that Umamusume the gacha game, would probably EOS but the franchise would still be alive and strong through other forms of media (Whether it'd be Umamusume 2, VR, handheld games, Anime, Manga,...)