Like... You know how at Tanabata, you write wishes and thoughts on paper, and then send them down the river or burn them? [and, pushing ahead, just in case she doesn't] Well... Maybe we could write goodbyes to Nakama-san. That way we're still putting our thoughts out there and showing that we care.
It's not the same, but since she might come back someday, that's okay, don't you think?