He's been great, I'm not denying that.
Projecting forward there just aren't very many forwards that continue to be good into their 30s and he's going to get overpaid by someone because that's just what happens. Maybe it's worth it for the Capitals to overpay him in order to get a few more years of production and extend their window and maybe he'll take a slight discount to stay in DC, but it's incredibly unlikely that he will live up to his contract for the duration. He's been dinged up quite a bit this year (including a concussion) and his production is being buoyed by an unsustainable shooting percentage that he will likely never replicate. Those items give me pause when offering a very long contract to a player whose best years are behind him.
If the argument is that he hustles and plays defense, then sign a high-energy grinder to replace him. His value is in his offensive production and I just can't see his production continuing to the tune of 6 years+, $6M+ that he will likely command.