Re: help with dead hive
Unless the hive died of AFB you can use it again. Is there any brood in the hive and if so can you post a pic of it? If the hive died of AFB there will be dead brood because AFB kills the hive by killing the brood and towards the end the bees do not have the strength to clear out the remaining dead brood. But don't panic if there is dead brood, other issues can cause this too, that's why we need a pic.
Re - what you could have done to save the hive, a recent study has found that varroa mites are implicated in the majority of winter losses. So, the obvious questions are did you monitor varroa or look for danger signs last fall, and did you treat the hive for mites and if so with what?
44 years, been commercial, outfits up to 4000 hives, now 120 hives and 200 nucs as a hobby, selling bees. T (mostly).