I really don't see Messi at another club so I don't know. Inter did comment that they have no plans to pursue him. I don't even think many clubs would get a look in if he was interested in playing elsewhere. I could see him following an old coach like Guardiola.See their are rumors of Messi going to Inter and starting another rivalry with Ronaldo but I personally don't see it happening. Griezman hasn't been the same since he left Athletico and the rest are just good players, nothing too great.
If Messi leaves, I see that team struggling for a bit.
They've got a decent team, the problem with them (as it has been for many years) is the defence. They've got a fucking solid goalkeeper (albeit not prone to his own stupidity), Pique is just a liability nowadays and Jordi Alba is an attacking wide back, so they don't really have a presence at the back. They need character. You know what, to be fair, Lenglet is good.
Now imagine instead of wasting those hundreds of millions, they'd bought a top centre back like Laporte before he joined Man City.