I totally agree, and will never understand why some people think it's ok to do that! At times, when it had happened to me and I would later see that person in person, I would try to be joking about it and making it sound like it didn't affect me, and they would reply ''yeah, I didn't know what to reply''... Well, for me, even if i don't know what to reply, I either put a thumbs up, or say ''I don't know what to reply here'', or something. Not just plain ................ (life line being deadddddddddddddddd.....)
Other times I have not seen the person in person to 'joke' about their 'disappearing act'... but after a few following messages with no 'responses', I get the drift... I will try again recontacting them a week or so after their initial silence, then about a few months later (so I will only write back 2 or so times more), then usually delete/block them after 6 months- 1 year of silence... I'm usually pretty patient.... (too patient I think!)