#3 Lower expectations
Whether Lionel Messi stays or not, La Liga and Copa del Rey should be Barcelona's main objective next season. Barcelona should forget that the Champions League exists for at least two seasons. That's how long it will take for them to at least seriously challenge for it once again.
The truth is that Messi's obsession with the Champions League has shifted Barcelona's focus from the most important title for the Catalans, La Liga. Yes, winning seven out of ten in the last decade may have taken the shine off the trophy. But that does not mean it should be taken for granted. The humiliation of Bayern could have been a softer blow had Barcelona won the La Liga title.
Just look at Bayern. They were 4th when Hansi Flick took over. They then marched to the title and that momentum is what they carried into the Champions League. If you cannot beat the teams in your own league, how are you supposed to stand a chance against the champions of other leagues?
Barcelona needs to start dominating the La Liga once again. Just like they did during Pep Guardiola's era. Only then can they even dream about winning the Champions League title once again.
#4 Tactical overhaul at Barcelona
There is a sad truth in Bartemou's Expendables. Though players like Busquets, Alba, Pique, and Suarez are legends of the club, they have lost their form in the last few seasons. They are all above 30 now, and in footballing terms that is old age. Only Lionel Messi and Cristiano Ronaldo defy that rule. So, hurtful as it is to say this, they need to step aside for younger players.
But just personnel changes wouldn't do it. Barcelona's problems started way before the aforementioned players losing their form. The high press nature of Barcelona has come to bite them in the back (literally) many times. How many times has Barca been left thin at the back by a diagonal ball across the field? How many times have speedy players (like Alphonso Davies) turned Barcelona's wingbacks inside out and fed the ball to the middle for a goal?
The key to playing high press is keeping the ball at all times. And if you lose possession, you must win it back almost immediately. If you even give five seconds, top teams will punish you.
While this sort of football is generally attacking, without the lack of a strong defense, it will crumble. When the wingbacks go marauding down the last third, you need to make sure that ample cover is given in case they lose the ball. You cannot expect the wingbacks to come running back to defend as soon as the ball is lost.
The best tactic though, is to find one that suits the players you have. High press and attacking football needs high stamina and concentration. If the players cannot do it, find a tactic that suits them. There is no Barcelona way. No use of Cruyffismo if the players cannot follow it. No use of beautiful football if that brings results like 8-2. Barcelona has been playing all style no substance football. That is not the Barca way.
#5 Do NOT replace Lionel Messi
This is the most important step. Lionel Messi may leave, and Barcelona may get a lot of money. Money enough that people like Bartemou may think they can buy any player in the world to replace Messi (looking squarely at you Neymar). But here is the thing, Lionel Messi is one of a kind, and replacing him is impossible.
In fact, that is true with every football player. Barcelona tried to "replace" Neymar, and in the end, wasted all that money in players who were just not ready. Dembele, Coutinho, and Griezmann are all good players but they just aren't Neymar. It has nothing to do with talent. They all just have different styles.
Instead of using the money to "replace" Lionel Messi, use it to strengthen other areas of the squad. A striker is essential even with Suarez and Griezmann. Bring in a good right-back and left-back who will actually start games. Barcelona had a certain Cucurella in their squad, a perfect successor to Alba. Even after he proved himself at Getafe, Barcelona chose to sell him. A worthy backup to Ter Stegen is also required, so that he feels the heat next time he misplaces a pass.
Keeping Coutinho can help Barcelona. Yes he flopped for two seasons. But in Messi's absence, he can be the playmaker he was at Liverpool. If you pay over $100 million for a player, you need to use him properly. He should be starting along with De Jong and Pjanic. If the board cannot remove the itch of selling Coutinho and successfully find him a newclub, then start Riqui Puig. He is a gem and one that has the potential to terrorize defences in the future; if handled well.