Eh, not necessarily, I've heard that one thing patent owners do is keep the thing ticking over by patenting something else sufficiently close to the original that they overlap and sufficiently different that they can be argued as distinct. Sure it's infringing - but it's infringing their own stuff. So, not invalid.

Note: as to whether any particular tactic like this stands up in court or not, you'll find out if you fight it in court. You and your huge heap of cash, that is. Don't have a huge heap of cash? Then the question is moot, isn't it, peasant?