Deferring more wages makes no sense for Barca as they'll just owe him even more in a few years which they'll have no chance of paying.
I think you're doing all you can to convince yourself that this isn't going to happen. Now thats fair enough, as United fans we've been lured into several BS transfers where we've been used and led on, but this is a case where Barca need him gone. He needs to take a pay cut, not another pay deferral. It just won't happen. It literally will be kicking the can down the road, and if he has a shite season, his value will drop, his deferred wages will increase and he'd be impossible to transfer, even more so than he is now.
If they defer any more wages, they'd be oweing him an absurd amount of money, you'd be looking at around €750k a week or so in the final year or so of his contract. Why would they do that?