What to do?
In the event it was NOT a reportable disease then:
Clean up and recover what you can. If it was mice then re-think your mouse guarding. If the combs are reasonable then fumigate. Look up Acetic acid.
Suffocation: then really! Re-think the ventilation you gave them and give them a LOT more the next time you move them. Then as above.
Starvation, well ponder your feeding and next time use a super and put on a chunk of candy/fondant on the top bars and fill the space with a blanket or other warm material. By chunk I mean three or four kilos. NOT a wee drappie please, FEED them not tease them.
If they died over winter with a full brood box of stores and no disease issues, and yes this can and DOES happen then be thankful as Mother Nature has culled a colony with poor wintering ability which is to your benefit and everyone elses. Yes it’s tough at the time but try to see the bigger picture.