Death grip is the result of needing extra friction to stay erect because you are desensitized. The underlying issue is desensitization and conditioning your sexual response to a screen. As you take a break from stimulation, you will not need to use death grip and masturbation will seem much more effortless. But, in short, stay away from death grip.
Fantasy might potentially reinforce those old porn-related pathways in the brain as you recovering, so it's best that you give it a rest. But by itself, fantasy will not cause you to have ED!!!
Once your reboot is done, you can probably fantasize about real women. Of course, this is tricky when you've been wiring your brain to porn from a young age. But gaining sexual experience with real partners will help with this. Now, if you have a moral objection to fantasizing about others, that's another issue. But I really don't see much of a problem with it.