He is later seen outside Fort Dawnguard practicing with his crossbow. When asked about the weapon he mentions it is common for people not to be familiar with it, as it is a Dawnguard specialty; however, he will give the Dragonborn a standard crossbow and some steel bolts to try out.
Upon completion of "Prophet," he becomes available as a follower. If the Dragonborn is not an Orc and hasn't become Blood-Kin through some other means, he will also send word to Orc Strongholds throughout Skyrim, so that they allow the Dragonborn entry.
It is possible for Durak to get killed during "Kindred Judgment." To avoid this, it is recommended for the Dragonborn to face Harkon immediately and skip all the fights with other vampires as all of them will be killed upon the completion of the quest.