That means you have option c) 2 standalone controllers.
That is the worst way to do redundancy as they don't share anything between them.
Also means you have to manualy do every configuration twice right? Nothing gets synced between those 2 controllers.
You realy should change this imho. And if both controllers have the same config then that is a pretty easy change for you to make as vlans and such are already done. What is left is linking them.
See https://www.youtube.com/watch?v=bE3tst09-RM for a very quick video on how to do this. From there you could start configuring high avalability. master-local + HA would increase your failovertimes and user disruption considerably.
Mind you, chaning a controllers role requires a reboot of said controller.
All this does NOT change the fact that with 2x Aruba6000/M3 controllers you can only bring up 512 APs if you want redundancy for them.
If you need more you'll either have to give up some AP redundancy or buy more/bigger controllers.
Since the Aruba6000 is end of life, you may wamt to look into replacing them all together for a set of controllers that can take the require load.
If budget prohibits that, you could extand the life of your setup by adding additonal controller(s) to your current setup.
While we do our best to provide correct info on these forums, we are nu replacement for a confident and knowledgeable engineer onsite, so keep that in mind before you start tinkering on critical equipement.