Just a few days after the injury, Kadri had surgery to repair the damage to his thumb and while the Avalanche said he was out indefinitely, they did not say he was out for the remainder of the playoffs.
For him to return, it would depend on his ability to hold a stick, stick handle, shoot and pass and how comfortable he feels doing so with a brace. Kadri returning would potentially provide the Avs with a huge boost, both matchup wise and from an energy perspective. There's no doubt that the Avs are a better team with Kadri in the lineup than without.