Depends on lots of factors. If for example the player has a spouse on a decent wage as well and the spouse just puts all of their wages away in safe investments for 15 years, they should be pretty close to being financially secure when the player retires. But that's assuming a full 15 year career on an average of £7k a week. That's a big assumption, especially looking at people like Josh Benson. It also assumes that the player has his head screwed on and is receiving sound financial advice - both of which are very far from a given. The other thing people are forgetting is that footballers are usually only offered mortgages for 10 years. A 90% mortgage on a £750k house over 10 years works out at around £7k a month. That's a pretty big chunk out of your £16k take home. Still perfectly affordable, but all of a sudden you've got a lot less to invest in the future, especially if you've got a couple of kids and a partner who chooses not to work. And while £750k obviously buys you something pretty impressive up north, if you're based in London and the surrounding areas you won't be getting anything particularly luxurious for under a million.
Very few league 1 players would average £7k a week for more then 4 years, take a look at our players, out of all the first team squad a large amount if not most won’t be on 7k and we supposedly have had bigger budgets than most of L1.
I'm not saying it's a poor salary - it's clearly not. But that doesn't necessarily mean it's big enough to allow someone never to have to work again after 10-15 years.