De Jong does want to stay at Barcelona, and his salary is higher than some other players, making him a burden on the team, especially since he can no longer contribute optimally due to frequent injuries.
Barcelona has been trying to sell De Jong since last season, but he still wants to stay, meaning the team management must respect his contractual obligations.
Overall, Barcelona's players are quite good in all lines and some of the substitutes also have the same quality, so I don't see De Jong having a big impact on the team, it's just a contract issue, so whether Barcelona wants to or not, they have to keep De Jong.
He can stay one more year with such salary, that is it. Next summer, his contract will be over and that is it for him with this salary. Either he will pay for a smaller amount at Barcelona, or he will go to another team and play for a smaller amount yet again. Only possibility of him playing decently would would going to Saudi league, then he could keep making about the same money or maybe a lot more.
However, plenty of people are missing that part of it and they are just assuming he would do alright. I am sure we are going to see Barcelona offer him something, but a lot less than what he is getting right now, could be same for Lewandowski too, those are getting paid a lot ,and maybe it made sense when they were signed, but not anymore so it should be less.