I also think never. It's a fact that Sambora doesn't want to be in the band anymore. But it's getting obvious that neither the band/Jon want him back, he managed to create too much chaos on them and I'm not referring only to the sudden mid-tour split of 2013. IF he announced to leave during a break where no tour was running and without breaking the contract so badly, then it would be much easier to come back.

The only reason that the band would want Richard back is that he is too loved by the fans. Except this one? I don't think this reason is too strong anymore since John Shanks and Phil Xenidis proved to be great guitarists.