Looking throught CC FAQ I found this:
I currently have a previous, perpetual-licensed Creative Suite edition on my computer. Will I be able to use both my Creative Suite products and the new Creative Cloud applications on my computer?
Yes, your existing Creative Suite installation will not be affected by installing the new CC applications. For example, you can install and use both Photoshop CS6 and Photoshop CC on the same computer.
Good news. I will always be able to go back to CS6 even if I decide to try out the cloud for the special first year pricing.
Also saw this in the 5 Myths post on the CC website:
You will need to be online when you install and license your software. If you have an annual membership, you’ll be asked to connect to the web to validate your software licenses every 30 days. However, you’ll be able to use products for 180 days even if you’re offline.
So, they give you a little wiggle room on the monthly subscription validation.