First off - I'm so sorry for your loss. I can't imagine the pain you two have been through.
I think you are, however, in the perfect position to step down without raising an eyebrow. You and your wife likely have a lot on your minds and I don't think you'll get much resistance if you step down as an elder in order to have more time to cope and tend to your wife's and your own emotional well being. I suspect that'll be relatively easy.
Next step is the tough one. Telling your wife that you no longer believe is a difficult conversation that no one wants to have and its impossible for any of us here to tell you the right way to go about it. You know your wife better than anyone, so I would just advise you to read what you get here and evaluate how you see it fitting with your wife's personality and her connection to the cult.
Many have had success with slowly planting seeds with their spouse resulting in an eventual awakening. Some have just come out in one fell swoop, and that sometimes leads to the spouse waking up and sometimes it leads to separation/divorce. In my case, I tried planting seeds for about a year before I had a big blow-up with the wife and came out about my non-belief. While I doubt that she would have woken up either way, I think it would've gone far better had I been up-front with her about everything from the beginning.
Whatever happens, know you're not alone in any of this. I wish you the best of luck in everything you're dealing with.