I never said that Lewandowski and Messi could end up having any problems with each other. On the contrary, I think Lewandowski knows about Messi's excellent skills to provide assists and every offender can only dream of playing with Messi as he developed into a real team player who is not so much after scoring himself anymore. He could be a real improvement for Barcelona's game as he adds the surprise effect because he still has the speed and the precision to create game situations like nobody else and also nobody can anticipate.
The jersey sales are one option and perhaps Barcelona sponsors would also help finance such a deal, but there will be financial limits even with sponsors involved. But maybe Messi already thinks about the time after his career and wants to make a step towards Barcelona now. But will he really forego the opportunity to make a couple of hundred of millions going abroad?
There is no doubt if we have Robert Lewandowski and Lionel Messi in Barcelona for the next season this could be deadly combo even I can say here this could be more lethal from Mbappé, Neymar and Messi in PSG because both players have amazing body language and things could be at his peak but this all need FFP approval which is surely not easy for Barcelona because they are already under huge debut and if they want to bring him back then surely need to offload few other players as well because their current salaries budget is already under problems which needs quick settlement these all issues are going against this combo.
But, if somehow Barcelona able to have them in their team at same time then we can expect amazing work and games against top team in La Liga and Champions League as well as hype is going nothing is clear because no one can predict where Messi is going to land for the next season and FFP problem allow Barcelona to have this player back into team.
If everyone were to play to the best of their abilities, Messi, Mbappe and Neymar should be more efficient than Lewandowski and Messi. Whatever the outcome may be of the next transfer window, Messi and Lewandowski could work out, but only for a year or two. You usually don't want two people approaching 40 years of age to be the pivotal point of your game.
Barcelona has to be planning for the future as well. Messi can assist and he can still decide games, but as much as I like him and I also think that Lewandowski is great, the two playing together would still be a transition period into something new. Messi could hep with building something new though.