In a situation like this you should probably designate at least one alternate AP as the WDS backup AP. Have a look;
Role of the WDS Device
The WDS device performs several tasks on your wireless LAN:
Advertises its WDS capability and participates in electing the best WDS device for your wireless LAN. When you configure your wireless LAN for WDS, you set up one device as the main WDS candidate and one or more additional devices as backup WDS candidates. If the main WDS device goes off line, one of the backup WDS devices takes its place.
Q. How many WDS backup candidates can I have? Can a WDS backup candidate still function as an AP in the WDS and report the information to the primary WDS?
A. There is no limit to the number of WDS backup candidates. Yes, the backup candidates still function as APs that report to the WDS master. In addition, only the primary WDS AP establishes WLSE security keys and registers with the WLSE in order to interact with the WLSE. Only if the primary WDS fails, the backup WDS takes up the role of an active WDS AP and goes on to register with the WLSE and establish security keys. As long as the primary WDS is active, the primary WDS functions as a normal AP that reports to the WDS master.
Q. If I have three WDS APs and they all fail, does the failure only affect WDS information, or all APs and clients? In other words, is the WDS a point of failure for the wireless network?
A. If your WDS masters fail, all APs fail as well. However, if the APs have all the configurations that are necessary for the AP to function independently, the APs begin to work without the WDS when the WDS device fails.