Sony owns the IP, they produced the game, if they want to use the IP then they can in another game.
From would have to get Sony's permission, buy the IP from Sony or do like they did with Souls and make a spiritual successor to Bloodborne, with it's own name and make it distinct enough from that IP to be able to release the game as a multiplat.
Sony and From have a great relationship, I'm sure both would be mutually interested in making a sequel if the game sells well and especially after how well the game's been received by reviewers and those that have played it.
As for anyone buying From Software, they're not privately owned, they're actually owned by Kadokawa Dwango, if Kadokawa wanted to sell then they're up for grabs, but I doubt they would.
