Hello,
FlexConnect is not a redundancy mechanism, it has several different operational modes, depending on how the authentication is performed and the data traffic is handled.
We might have Central Switching, Local Switching, Central Authentication or Local Authentication, and there could be a mixture of all these methods, for example you can do Local Switching with Central Authentication, or Local Switching with Local Authentication.
Also, depending on the security mechanism used, the behavior is going to be different if you use a Preshared Key, or if you use a stronger method like radius authentication (802.1x).
With FlexConnect, if the APs is dissasociated from the WLC, it might work in standalone mode, but the wireless clients will have different behavior depending on the Flex flavors mentioned above. For example, if you are doing Central Switching and the AP goes into standalone mode, all the clients will simply stop passing traffic.
If you are doing Local Switching and Central Authentication, the wireless clients will remain associated until the session times out, then the client won't be able to re-authenticate or can't roam to other AP, APs won't accept new clients.
There are just a few scenarios on which the AP can keep the existing clients and associate new ones, so thinking on using FlexConnect as a real solution for redundancy, is not something very reliable.
However, you can analyze if there is a way to accomplish this with any of the FlexConnect methods, if you really want to think on using this approach, is better to read this guide first:
http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob73dg/emob73/ch7_HREA.html
Newer codes introduced more features on FlexConnect, so it might be that you found a way to do this configuration to work. This is the configuration guide of version 8.0:
http://www.cisco.com/c/en/us/td/docs/wireless/controller/8-0/configuration-guide/b_cg80/b_cg80_chapter_010001000.html
Hope this helps
