Best hope is that this is just a throw away year and he returns to his normal levels next season. There have been many instances of guys having throw away seasons where everything goes wrong, and then are able to bounce back. Yes, there are Mike York types that never recover, and that is possible, but not a guarantee.
Luc had a couple of very down years while he was still in his prime, and bounced back to be an all-NHL performer again.
Justin Williams had a rough couple of years, maybe chalk it up to injuries but his production was way down, I believe he was even healthy scratched for a playoff game in either 2010 or 2011.
Trevor Zegras is having a throw away season right now, yes he's been hurt but even when he was healthy he wasn't playing well. I'm guessing he will find his way back to the 60+ point 2nd liner he was before.
Alexander Mogilny in his late 20's hit a career rut, actually had multiple seasons below standard and then returned to stardom with the Devils and Leafs. PLD doesn't have the talent Mogilny had, but he appears to have many similar attitude traits.
Teemu Selanne with the Avalanche was a complete throw away season, and he came back to his previous levels with the Ducks.
I don't think all hope is completely lost.