William Cage never seems to make it longer than the day of the France invasion. If he were to survive longer than that (a week) would he still have the Mimic power, and would he still revert back to the morning before the invasion?
In both the book and the film, his power seems to result in him resetting to the same point, regardless of how long he's been alive since. His trip to France (and subsequent attempt to attack the dam) presumably took considerably longer than 24 hours and yet he still ended up back at Heathrow when he died.
Unlike Groundhog Day where the hero reverts magically at the same time each day, Cage seems to revert instantly on the moment of his death to a point approximately 24 hours before he killed the Alpha in his first iteration.