I see that's the main point isn't asking for like button, but it's about the end of discussion matter.
Because the discussion gets stuck, and if someone doesn't reply again I don't know if they agree, don't care or haven't read my reply. This is annoying for me, especially when it involves important things. At least if he gives a tag that he read but does not reply it can be concluded that the discussion is over (with or without agreement)
Show me few examples where you think it's important and the user need to reply your post.
No one owe you anything, it's up to the user still want to continue the discussion or not. Even the user is using telegram bot and you keep mention his username, he don't have to reply your post.
Sending a private message isn't a good choice, he can report your message as unsolicited message and you risk a chance to get temporary banned.
Just assume the user have read your post and move on.