Implementing session persistence in Active/Active GSLB even when the LDNS changes during the session. How to?

What kind of load balancing method are you using in the WIP/Pool ? If you are using some kind of topology/geo-location based load balancing, even with LDNS change, the DNS request will probably be balanced to the same Virtual Server.

If you combine the above with cookie based persistence at the LTM level and same IP addressing scheme at the server level, you can make sure that the request is being sent to similar server.

You can also set up the server to insert a cookie or header information that can provide information on the datacenter location or VS and using this and an iRule, you can send a redirect, if the request is sent to the VS in other DC.