A few minutes ago I was mining in outland and found a fel iron deposit without fel iron in it, I giggled because it reminded me of the days when you could go around partially mining titanium [aka taking the titanium and leaving the rest behind to troll any unsuspecting prospector (you did it too, don't deny it)]
But then I found another one, and another, and I got chills down my spine, so I tried it myself in the next 2 deposits and partially mining worked, I did a quick search in the bug tracker and found nothing related, at the moment I need to head out so I can't fill in a report myself, and it would have to be tested in northrend/classics zones first, tomorrow I'll set to the task of further testing/reporting, in the mean time I'll leave this here for anyone to read
TL;DR: partially mining without despawning deposits may be back, however I can't test it any further today, please report it if is true because this could break the economy