What to do about unlimited time game and opponent does not return?

Is there any way to have an unlimited time game cancelled when the opponent doesn't return? I was in this type of game, playing interactively (not much time between moves) and when it became clear that the other person was going to lose the game, they just left and have not returned. Seems like the game is in 'limbo'. Is there a 'reasonable' amount of time that needs to be waited?

I think he/she will lose if he/she does not move in 1 month

@JoeFonte I think I remember that @thibault once said to only play unlimited games with people you know, because it truly is unlimited. I'm not positive though. Have you messaged your opponent?

I have a game that's been going for a while with my opponent not moving. Pride doesn't allow me to resign. I think I still have another 60 years left on this earth God willing, so I will wait. You hear me @tuckfinn. You will get crushed! In this life or the next! You are only putting off the inevitable.

Thanks for the input. Much appreciated.
A month sounds reasonable enough (hope that works V1chess). I've also just sent a message (thanks for the tip Jacob531).
I'm new to Lichess, so I'm still trying to learn how to navigate the site and figure out what the 'norms' are.
No more unlimited games with strangers (kinda like candy from a stranger - I guess).

Now I know what the at sign does in front of names. Learning...
Thanks @V1chess and @Jacob531.
I feel ya @NeverBeenTimid.

You bet. By the way, you can message @luciano_the_best and ask for the link to a YouTube video he made as a lichess guide. It might help some.