WordPress Plan Question

Does anyone know what will happen if you choose NOT to renew your paid WordPress plan? Will you go back to the free version and still be able to post and see past posts, or will you lose it all? When I started on WordPress, it was free, except for the fee I paid annually (about $20) to get my own domain name.

I still pay the domain name fee. However, I was considering letting my Personal WordPress plan expire next month (the one that costs $4 a month). I started using an upgraded plan because I wanted a chance at getting ad money, but it just isn’t worth it as the ads don’t pay much of anything and I spend more on the membership plan than the ad revenue I get back.

Have any of you recently cancelled a paid WordPress plan and went back to a free blog? If so, how did the transition go. Did any important changes happen I should be aware of?