TL;DR: Allow users to flag when someone they're talking to has ghosted them; potentially showing it on their profile if the user is consistently flagged. Maybe this is a premium feature.

Allow users to flag when a user with whom they've established a dialogue (setting an objective threshold to be exceeded e.g. an exchange of two or more messages from each user on at least two separate days*) has abruptly ceased contact with them (i.e. ghosting).

Consider showing which users are consistently flagged as a premium upgrade or subjecting consistently flagged users to a cooldown on sending new messages if it is a recurring problem (as ghosting cannot possibly be good for someone's mental health; I'm sure there's data on this**, but it is harmful, wreckless, and potentially dangerous behavior). A distinction must be made between users who ghost each other and conversations that just fizzle out. Consider only escalating to the premium flagging or cooldown option if a threshold is exceeded. This might be a percentage of their active dialogues (but you'd have to define "active".

You would also need to account for the passage of time. Anyone on the platform long enough is probably going to ghost X amount of people, so maybe this only applies to flags issued within a given period of time.

Maybe more specifically two separate 24-hour periods or something to account for communications taking place immediately before and after midnight.
*If there isn't data on this, then there absolutely needs to be.