Unfortunately it looks like the game will be coming to an end. Disney has announced that they will be parting ways with the developers of the game, Gazillion Entertainment, which will effectively see the game come to an end at the end of the year where the servers will be officially shutting down.
In an email sent to Kotaku, “We regret to inform our Marvel Heroes fans that we have ended our relationship with Gazillion Entertainment, and that the Marvel Heroes games will be shut down. We would like to sincerely thank the players who joined the Marvel Heroes community, and will provide any further updates as they become available.”
The game was originally released in 2013 where some have compared it to RPG titles such a Diablo. There have been some signs leading up to the announcement that the game could be on its way out, such as community updates not being posted, missing out on a Halloween and Thor: Ragnarok in-game event, and how several community managers on the forums stopped posting.