If the debts aren't sustainable you're gambling on something to happen. Ah, i'm spending more money than i earn, but if i just win the lottery or somehow start making more money in the future...
Barcelona have fecked up, quite a lot. Insane fees and wages spent on players that have failed miserably at the club. The most high profile ones are Coutinho, Dembele and Griezmann, but that's just the tip of the iceberg.
If the club is so badly fecked, that they reckon the loss of Messi would be so big for the club that it would also have an dramatic effect on the clubs overall income, and as a result they are willing to give him an obscene wage they can't really afford, then they need to re-evaluate things rather quickly.
In terms of Messi, he's been one of the best paid and most successfull athletes for years. It's not like he's been underpaid compared to what he could've made at another club, there's barely a club that could even come close to what Barcelona have been paying the fecker. His wages are detrimental to the club he's been in for ages but the club is seemingly desperate for him to stay. It's rather bizarre that there's so little focus on it. If he wants to feck off to another club, then by all means, no issues whatsoever, but if he's playing the waiting game in order to get as much as possible from Barcelona then it's beyond me how supporters can get behind him.