I've been roleplaying for more than 25 years, but it really is a thing of very recent to not reply to either a PM, or stopping an ongoing play totally out of the blue.
or stopping an ongoing play totally out of the blue
This! This right here! lol
I don't so much mind if I reach out to someone and they don't reply. That pretty much tells me all I need to know about the person (i.e. he or she isn't worth my time). I will always try to let someone know if I don't think it's going to work out and I might not think it's going to work out and still give it a try just in case I'm wrong! However, I hate it when I've agreed to play with someone and they just drop the story without telling me. That bugs the hell out of me. I will always understand if someone comes to me and says, "This one isn't working out. I'd rather not continue." I respect that so much. I respect it if someone tells me that something has come up and they are going to take awhile to post. However, if someone just stops responding, I always make a note that this person may not be someone I want to have contact with in the future unless they come back and explain that something IRL happened that prevented them from continuing (I've had that happen, myself). I've even instituted a rule for myself that if I send a post and two weeks goes by and I don't hear back from them, I'm going to just assume that the story is finished and I'll re-post that character/story to see if anyone else has interest. I understand that some of that may be harsh, but I'm too old for all of that.
But, yeah, I understand the feeling that it's a little on the rude side if someone doesn't just shoot you a message letting you know they aren't interested.