What happened to the other Leviathan besides Dick?
In season 8, Castiel was being hunted by Leviathan in Purgatory even though only one Leviathan actually died in season 7. My theories on why more than one Leviathan appeared in Purgatory are...
a. Crowley claimed that Leviathan would become standard monsters after Dick died, so my guessing is that Leviathan hunters decapitated would actually die when they were no longer Leviathan and were just ordinary monsters.
b. Is it possible not all Leviathan escaped? I mean we know Eve did not escape (or do we?) but has this ever been considered?
Here is one random theory, I think Eve escaped Purgatory due to her having enough power to hold onto Castiel. And maybe she learned her mistake of making herself immediately known, so maybe she went under the radar.