I can't think of a single player who left us as an established top player and then was just as successful somewhere else. They all ended up playing less, scoring less, and often leave again.
With less senior players it sometimes happens - some players we basically let go and they carve out decent careers elsewhere, but not in a top team - Coady for example, or Shelvey.
The only player left us and had good success elsewhere is probably Sterling, and he was still a bit of a youth player when he left.
Yeah there's a fair few that people have named....but none of them left when we were really at our best either. I think thats the kicker here. Owen, Torres, Alonso, Masch, Suarez, Sterling, Stevie. They all left when we were either at a bit of a low ebb (Owen, Torres, Masch, Sterling, Stevie), left because we clearly didn't have the resources to kick on (Xabi) or left after a bit of a freak season when he was the catalyst (Suarez).
When they left it was always a bit of a case of 'fucking hell what does that leave us with?'. If Mo decides to go (still dont think he will) we can do the same and go 'Okay Alisson, Trent, Virg, Ibou, Robbo, Thiago, Fab, Naby, Diaz, Mane, Bobby, Diogo and more AND a load of really promising kids AND an amazing manager who has just extended his contract. We are in a much, much stronger position than when any of those guys left.