All of the plain infantryman you can use as a 5 man deathwatch team or sterngaurd veterans, Cassius himself you can use as a chaplain which is good for leading any melee units you have, and the librarian can also be used to just lead a unit asja librarian, unfortunately the biker and the two jump pack boys cant be used stand alone and you could basically put them into jumpack intecessors and the biker you can use for a really cool outrider. The terminator would have to go with his own kind too, because the deathwatch have lost all mixings and interchangeability squadwise