Make Spooky Gangplank his new Classic, and the current base a temporarily free "Captain Gangplank"
I really don't want a deux ex machina to revive Gangplank, which I personally hate in stories and I feel would ruin the otherwise so-far brilliant Bilgewater story. Why not just make Spooky Gangplank his new base splash art? And his current base would be a skin called "Captain Gangplank" that would be free for anyone currently owning Gangplank a week after the Bilgewater event. After it would be priced 520 RP.