In case you forget, Nichushkin left Seattle in the middle of the series against the Kraken. There were little details released at the time, just that he was ushered to the airport with a security detail. A police report later revealed that an intoxicated woman was in Nichushkin's hotel room, and an ambulance needed to be called for her.
There was no NHL investigation into the matter that occurred with Nichushkin, as the NHL determined that Colorado and their staff handled the incident appropriately. As such, he is fully eligible to play this season with the Avalanche.
The team doctor who called the ambulance, however, is no longer with the team. There were no comments made to confirm why they were let go or whose decision it was to let them go.