NB: The only penalty is inability to mine blocks within some period of time. They still can decide not to bother with mining, but their "hashing" power will be distributed to those who do protect the network.
Due to the redistribution of "hashing power", is there any chance for someone who holds less than 50% attack the network?
Say, 50% of the coins are "dead" (never mining), the max of which holds 27% of total coins. Now the other 50% coins are mining, and the max holding of which is 26% of the total coins, will this 26% ( more than 50% of the redistribution power) attack the network? Is the network monitoring the maximum "alive power"? Hmm, very interesting, the dynamic PoS mining power network!