New pricing question - Downgrade to free?

I currently am paying for the $20 TKL pricing level (and have been for a few years now)... But I just discovered that it looks like unlimited T1 instances are available for the free plan now. If we could get by on just T1's until business picks up, can I downgrade to the FREE plan without any of my T1 servers dying on me? And then upgrade to the $20 plan when we need the Small and Medium servers again? I just don't know enough about the ramifications on my servers when I hit that 'downgrade' button. Does amazon simply terminate all instances that aren't covered by the plan any more?