Well, they would realize that all merchants are simply locked out of all transactions, unless merchants use the new rule software on their full node, or connect their wallet to a miner node. Because there aren't any other transactions in accepted blocks.
So yes, miners can't cash out their coins, as long as ALL USERS decide not to upgrade, and accept being locked out of bitcoin, their funds and their transactions at the same time.
1. pools are not going to waste 16 hours to double prove what they learn in 3-seconds to 10 minutes.. which is they cannot spend funds
2. pools are not going to waste days/weeks/month to really trying to push it in the HOPE that nodes download a MD5 hashing rule implementation..
after all even core suggest it would take a year to get clear node acceptance..
reality is..
if there was some secret cartel of "lets make md5 blocks for the next 6 months to force nodes to be less secured"
initially 20 pools have that motive.. but soon enough a pool gets greedy and jumps back to sha256 and wins every block.