Barcelona might be financially trouble, but as long as they can get rid some. It's possible for them to sign Alvarez as a new striker.
Importantly, Lewandowski is getting older and need a regeneration. You can't always rely upon an old striker like him. There must be a backup for his position.
The young players they have today are core players and all of them give a fairly important role to the success of the club and if Barcelona makes the wrong decision by selling some of these players can have an impact on the depth of the squad. Barcelona does need an attacker to replace Lewandowski but also requires a balance so that they do not get problems with financial capabilities. This is what needs to be considered so that they don't get problems in the future like the incident must release Lionel Messi.