If we do get notification saying "A player has declined or left the champion select...", we don't have a button to close the notification. Only waiting can make it disappear. The notification actually blocks the "Loot" and "Store" button. I hope we get to close the notification like we used to in the legacy client.
Also, I do hope the feature to view the players you have played with recently would make itself into the new client. I'm sure I'm not the only one missing it.