Thank you for reaching out with this beekeeping question! I'm sorry to hear that you lost your colony. 

We don't have a lot of research or information on the risks of reusing combs from a deadout (unless the colony died from American foulbrood disease, which is uncommon). Many beekeepers reuse frames from dead colonies for new colonies in the spring without a problem. If you want to reduce potential risk, you can toss brood nest frames (since we expect some pathogens to build up in the brood nest). You can toss frames full of pollen, since pollen loses its nutritional value over time. We toss frames with excessive mold or bee poop or we scrape off the mold or bee poop. We also try to remove frames that are several years old, since pathogens and pesticides can build up in the combs over time. We tend to reuse frames with stored honey and syrup and empty comb. 

You can store frames in the freezer like you suggested. You may also be able to just leave the frames in the hive until next spring as long as you have entrance guards to keep mice and shrews out.

I saw that you had a varroa mite count of 9% in mid-September, which is pretty high!  We hope that most of the needed varroa mite management was already done earlier in the beekeeping season. As you may know, varroa mite levels are usually at low levels in the spring, and they build up in population through the summer and fall. As varroa mite loads increase, virus levels also increase. We attribute a lot of colony losses in the winter to these viruses. Even if your Formic Pro treatment in mid-September was effective at killing many varroa mites, we would expect the virus levels to remain high for months. Colonies with winter bees that develop in the fall under high virus pressure are often unable to survive. The varroa mite management that beekeepers do in the spring through fall may lower varroa mite and virus loads going into winter.

Our team discusses varroa mite management throughout the season in our Michigan Beekeeping Webinar Office Hours. Here is a link to the recordings: Michigan State University Beekeeping - YouTube.

We do occasionally see queen loss with Formic Pro treatments. I've used the treatment hundreds of times, and I think that some beekeepers may overstate the risk of queen loss. It is possible that you lost your queen late in the season from the treatment or just normal management. But based on what you shared about your mite levels in mid-September, I think it is most likely that your colony died from virus levels spread by varroa mites and a lack of healthy winter bees.

Many beekeepers lose colonies in winter due to viruses spread by varroa mites, so you aren't alone. Thanks for taking the time to send this question about reusing frames for the next beekeeping season!