If they have money to buy another defender, which they would clearly have, if they sell Silva to Barcelona, it means we could just try to buy that other defender is PSG doesn't want to sell him. Paying extra for him just isn't worth it, it's just a defender, we would end up paying 50 for goalkeepers, we should be a bit more cold and not look so desperate, everybody wants to sell to us for tons of cash so they could make a nice profit and buy only for modest sums of money, and as we suck, we usually do the worst, like giving Ibra for 24 ( 3x 8 million/season... ) after paying Eto'o + twice that money 1 year earlier.
We should try to sign someone else, at least for the show, maybe if Silva wants to come to Barcelona, PSG would be left with no other option than giving him up for a normal transfer sum.
So, screw him if he isn't available, we're talking about defenders here, you'll be surprised how many good central def's are in this world able to do the job, a defender isn't worth 50 million, ever, unless an egyptian god shows his face and tells you he will be a killer for 20+ years and he will be the guardian angel of your club for 2 decades.
I can surely tell you Vlad Chiriches is worth 5-6m and whoever buys him will do a bargain, he's probably the only Romanian player at the moment that is worth a good transfer sum

, there are others that are good but Vlad has potential, with some extra experience he will be able to play at any club in the world, that if someone like Chelsea or City doesn't buy him from the beginning and he settles from the start at a big club. He's 23, that's kindergarten age for his position.