First post has been updated with second attack, actually tested on Mintcoin.

As you can see here, the PoW blocks have a different and independent difficulty algorithm than PoS blocks. If you start getting a lot of PoS blocks in a row, the chance of PoW block generation increases in order to achieve the PoW target; so after each PoS block is generated the likely-hood of generating a PoW block as the next block goes up, and after every PoW block, the chance of generating a PoS block goes up. They are both integrated with block targets and difficulties that are independent of one another; ]so one cannot perpetually overpower the other.This is why PoS/PoW hybrid is more secure vs just PoS only. And, it is also worth noting that over time, the Mintcoin networks actually will get more secure with age, whereas a PoW only coin has the potential to get less secure due to centralized mining processes. Mintcoin is protected from PoW overpowering, as well as PoS overpowering. You cannot know for certain the future of the Mintcion blockchain (at least very far). With Pure PoS, you know the future will always be a PoS block next, and with PoW you know that the future will always be PoW blocks next, but you cannot know the future with hybrid PoW/PoS like Mintcoin.