If someone signs a message, I quote it (so it would stay even if he edits/deletes the post), he deletes it, my post gets deleted too?
As a example: If you just deleted the quoted post, my post would not make any sense at all.
It absolutely would. The content of the deleted post would still be there in your post, so anyone reading it will be able to understand and make sense of the contents.
If I deleted the post, your post would still make sense and the OP and any other who are interested in this topic and are reading it will be able to understand that quoting a post that later got deleted could get deleted too.
I still don't see why it should be removed just because the quoted post was deleted.
It could also imply that if an OP is edited as to suggest a significant change in topic, all the posts on the thread (especially the ones quoting OP) will become irrelevant and should be deleted
(Well all the posts would be off-topic, so it could be justified than the above case but do mods actually do that?)
It would.
It isn't like we are the only two persons in this forum. The content of the deleted post could be useful to anyone.
I am taking "might" to mean most of the time, such posts can be justified of getting (/deserve to be) deleted.