A few manuscripts of the Gospel of Mark insert two sentences in-between 16:8 and 16:9. They are known as the so-called "Short Ending" of Mark. Check them out. Some of your translations might make note.
Here the narrator basically reverses 16:8, reporting that the women eventually come around and do inform Peter and his companions of everything that the youth had commanded.
Then Jesus himself comes on the scene and commissions them to spread "the holy and incorruptible proclamation of eternal salvation" throughout the whole world.
By the way, all the manuscripts that record these two sentences go on to record 16:9-20 as well, except for one, which ends the gospel here, with the "Short Ending."