you can use everything like before, you just won't be able to upgrade to newer version of software or future SP of program.
As for getting back on subscription plan later - I know there are some changes like - if you drop out of subscription and then want to buy it again you would have to back pay for the time your subscription ended and when new one is to start - BUT some one would have to confirm it (as i'm not responsible for those things in my company)
It is my understanding that if you let your subscription expire you will be require to pay all the yearly subscriptions from when you stopped to when you want to restart the subscription not to exceed the cost of a new seat. Example: If you do not renew for three years you will be required to pay for 3 years subscriptions provided those 3 years do not exceed the cost of a new seat.
As Wayne and Wojciech indicated, if you do not renew and want to renew later, you will be required to "Back Pay" the subscription fee for the entire time you were off subscription - as long as that cost does not exceed the cost of a new seat. You will still be able to use your existing seat just as it is/was at the time your subscription expired. There is no time limit on how long you can use it. This is assuming you are not on a network license (those are NOT perpetual licenses). A standalone seat is a "Perpetual" license.
If your seat expired after a service pack or new year version was released, and if were on an earlier service pack or release, you will still be able to install and use the most current version and service pack that was available "at the time your subscription ended".
However, you will not be able to download these files if you do not have a current subscription, so - even if you don't update just before the end of your subscription - be sure to download the current version and service pack prior to your subscription ending.
If you can get the downloaded files from your VAR or another person that has, or can download them, then you can update your software with that - but again - only if it was released before your sub. ended.
There is another thing I need to mention that was not stated earlier. The renewal fee you will have to pay will be the subscription cost for the time you were OFF subscription PLUS you must pay for the next years subscription as you would normally do on a renewal. The old fee of $500 if you were renewing after your subscription had ended previously no longer exists.
If the cost of the backdating exceeds the cost of a new seat (of the same version you have (standard, pro or premium) then you will be purchasing a new seat (plus you will have to subscribe for the next year - as you would have done anyway on a renewal).
The cost of the new seats is approximately equal to 3.4 years of subscription cost (+/- 1/2 year).
The bottom line - if you plan to renew anytime in the next 4 years, you will benefit by maintaining your subscription - simply because you will be able to get current updates and have full access to the subscription features. If you don't renew for 2 years and then renew, you will be paying subscription fees for the entire time you were off subscription and you will not have gotten any of the subscription or VAR benefits. If you are happy with what you have now and plan to wait for 4 years minimum - then cost wise you should wait (but you get no updates or benefits of subscription).