For Kettani, he became expendable once the team signed fellow fullback James Develin. Teams seldom carry a fullback on their practice squad, so it's even more unlikely they'd carry two. You shouldn't rule out the former military man coming back later in the season, if injuries arise.
As for the re-signing of Warren, I couldn't be more pleased. In the cesspool that was the backup Patriots offensive lineman, the UDFA Warren held his own. He'll get (we assume) the full year on the practice squad to keep developing, and may stand a better chance of making the roster in his second season.
With their game not until Sunday, we could very well see more roster moves being made by the Patriots in the coming days.