I agree. Dude is 36 years old, very soon to be 37 years old in 2 months. So yeah, while he scored bunch of goals this season, how long could it even be going? We can't see him forever be scoring like this, it makes no sense and it would be near impossible. Either he is going to start being bad this season, or best case, the season after that.
Barcelona would have sold Lewandowski this season if they had found a suitable replacement for Lewandowski. Hansi FLick does not have a suitable replacement for Lewandowski. Despite talented players like Rafinha and Yamal being in the squad, Lewandowski is still Barcelona's leading scorer. So Barcelona management will not decide to sell Lewandowski before finding a suitable replacement.
Lewandowski has played very well this season. It can be expected that Lewandowski will continue such good performances for the next 2/1 season. Lewandowski's fitness is still good enough. However, Barcelona should find a replacement for Lewandowski now.