Not good news for Makar.
Here's the collision and it isn't event that major of one.
Really a shame such a talented kid is hurt again. This wasn't a failure of the NHL and there's no rule that could've prevented this. This appears to be a failure of the team's medical staff to judge Makar's initial recovery. I'm not accusing them of negligence, but there's an obvious knowledge-gap in how a brain recovers from concussions. Makar thought he was ready, the staff agreed, but they were both wrong.
Whatever protocols are used to determine when a player is good to go needs a serious rethink. If it's impossible to judge, err on the side of more caution.