Total Swedish Victory in Second Northern War

How the swedes could prevent the danes from intervening after the Treaty of Roskilde, capturing John Casimir II and securing the claim to the throne (recalling that the Lithuanian nobility had already ceded to Charles X Gustav)? That is, total victory in the Second Northern War.
 
How the swedes could prevent the danes from intervening after the Treaty of Roskilde, capturing John Casimir II and securing the claim to the throne (recalling that the Lithuanian nobility had already ceded to Charles X Gustav)? That is, total victory in the Second Northern War.

Let Frederik III fall down a stair in 1656. This is a perfect point, as the succession is clear with Christian V having been crowned heir in 1655, which mean Denmark will be ruled by a regency council until 1664. Killing off Frederik earlier would cause a election where the Duke of Gottorp would likely have been elected, which would result in a more active Denmark. Of course this just mean that Denmark doesn’t enter the war at all, it’s harder to avoid Denmark joining after the Roskilde Treaty, as it was Sweden which restarted the war after the Roskilde Treaty.
 
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