Check the contract. It's a one year commitment. You can use a trial version for 30 days for free. It's exactly the same as the paid version. There is no difference. If you are a full time student and you have credentials qualify for an educational discount and there is also no difference at all in the software. If you have any questions get someone from Adobe Sales on the phone and clarify before you buy.
Then what is the 12-month plan which is $15.99? The 1-month plan is $29.99.
To answer your initial question, if your subscription stops, the software will eventually stop working until your subscription becomes active again. You will not lose any files on your local machine though.
As far as pricing goes, talk with Adobe sales or look at the website from your computer. Because the pricing is different depending on where you live.