Well, the game can indeed survive without an active developer, as long as the community remains active, trading between players continues, the servers remain active, and no bugs are found that affect the economy or gameplay in general.
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All that is needed is a central orchestrator from the parent company (nabi) to handle the organization, recruitment, and management of the staff and events.
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But what can happen is exploitation by hackers without anyone ever discovering it if there isn't an active developer, either through the insertion of malicious code and scripts that only a developer with access to the game's code would be able to discover.
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Perhaps if the forum were disabled, it would help a lot, since a hacker attack on the forum could literally break the game... but it would also significantly affect and contribute to a faster decline in the game's standing with the community.