What??? Why do you need to close working MN? If my MN ceases to work on May 15th, I will sell all the coins and I will invest my money in more stable coins and stable developers.
If the collateral requirement changes how could they keep working? The protocol version will change so you can't avoid upgrading and if you upgrade the transaction will not be a valid collateral.
If you haven't been selling your earnings, which is the right thing to do given the abysmally low prices you should have enough to make the new collateral.