I am not sure that Lewandowski will get a lot of chances next season if he doesn't score a proper number of goals. It will also depend on their activity in the transfer market. But his star isn't rising anymore to say the least. He has his qualities, but speed is a big question in my opinion, I like how he plays and he can play a good style within teams that suit him, but I am not sure that Barcelona is still the style he can benefit from. They are more about a high technique level and speed and Lewandowski is getting older and slower. The next season might be the one where he realizes that he is probably sitting more on the bench than getting time on the pitch.
Age is a problem for Lewandowski and his performance is starting to decline, but in my opinion he is still worth keeping for the next season because he still deserves to play at a high level. But Barcelona is reportedly also targeting another striker to support Lewandowski. I think this decision is quite right because it could be an alternative between the two. However, so far we have not seen at all who will be the replacement figure for Xavi, because whoever will be the coach will really determine the game scheme implemented and the compatibility with the existing players so that Lewandowski's role will really depend on the new coach.
Yes, of course age has affected him so badly. There is no way he can deny the fact. I could remember back then when he could run so fast, strike without minding if he is going to have any injuries at the end. Its so painful that is coming to an end which he knows full well.
Bringing another striker to the team might work out well for them, but lets be honest how do you think the new striker would cope together in the pitch with Lewandowsky unless they will be starting the new striker instead of Lewandoski and then maybe during the second half they can bring him in to substitute and play for some time. Honestly he wont be Barcelona first choice of striker.