It’s a probabilities thing. Someone who’s stopped taking an interest COULD be doing so because they’ve had real life interfere and they are unable (for some reason) to give notice.
Alternatively it could just be someone who has lost interest and isn’t playing much and/or not bothering to monitor chat.
I expect the 2nd option is more likely.
I have had 1 member leave on the back of a warning in chat, but that had the support of the alliance as a whole because that person wasn’t contributing. I’ve also had a couple of members pull their socks up and start taking part.
I’d prefer the ability to private message members somehow (maybe restricted only to people in your alliance). It never feels ‘right’ to have to air dirty laundry in front of the alliance as a whole, but there’s no alternative, so that’s what I do. I feel a warning is more fair than a summary dismissal without notice.
(My Alliance = Aleph Null)