#the above information is a very broad summary of info from various academic and human rights resources and the relevant statutes

[kaurwreck]

If enough Kira worshipers demand for his release, even going as far as continue to making serious threat towards the goverment until they do, would Light be released? What are potential of him being released at all? I imagine Kira worshipers purposely making it difficult for anyone after the revelation

There are cultural, procedural, and common sense reasons why Japan's correctional organs would not be compelled to release a mass murderer with a preternatural capacity for serial killing who sought to destroy the social order to satisfy his god complex based on threats made by such mass murderer's riotous cult.

This isn't to say Kira worshippers wouldn't influence Light's sentencing. I'm sure they would since Japanese courts take into account the impact of a convicted person's crime(s) on Japanese society when determining whether the death penalty is appropriate, and instigating civil unrest that threatens national security constitutes a comically deleterious impact on Japanese society.

This also presumes a public and transparent process, but even where the circumstances aren't nearly so extraordinary, Japanese criminal proceedings are not terribly transparent. For example:

From the moment of arrest, prosecutors may strictly limit access to defendants; even defense counsel and family are often barred from contact.

Defense counsel has the right to request access to evidence the prosecutor uses in court, but the prosecution can withhold all other evidence. Further, defense counsel is only permitted to use disclosed evidence to prepare for trial, and cannot disclose information obtained during pre-trial discovery (including to the public).

Japan's constitution mandates open courts, but this does not extend to criminal court records, which are controlled by prosecutors and, if published, anonymized.

Japan’s death penalty law requires that executions must be carried out quietly and without public notice. Death-sentenced prisoners are kept in strict solitary confinement and monitored by 24-hour surveillance cameras. Prisoners are informed just one hour before their sentence is carried out, so their families and defense lawyers only learn about the execution after the fact.

Japanese prosecutors exercise immense discretion based on an opaque system of internal deliberation and consensus and, are substantially insulated from public scrutiny. This doesn't mean they're never influenced by the public, but its rare, and relatively weak.

tl;dr: (1) serious threats to a national government by fringe cultists are not usually a compelling criminal defense, but can be used to justify harsher sentencing; (2) there is 0 potential of Light being released if arrested, but very high potential for Ryuk becoming bored and killing Light before the Japanese government can get around to it. Which, isn't not canonically what happened.