I entered a 1v1 Howling Abyss blind pick, and we played to first blood. I closed the client, logged back in, and it still wants me to reconnect. Apparently the friend is finishing it to the end. I've logged out and in a few times now. I'm probably gonna have to wait for him to leave. I'm on Windows 10 home if it matters.
I know when I do a Me vs. AI custom match to test something, when I leave it will give me the Reconnect button, but when I press it I get a message that the game has ended and it returns me to the home page.
If your friend really was still in there, it's a given that the game will stay active and not let you join another yet, but most likely he did leave and when you press Reconnect it'll let you know the match is over instead of actually reconnecting.
