That's exactly what I did. It's really your only option.
Our 1000-plus member Yahoo group lost our owner 4 years prior to the Yahoo exodus. I asked questions in the group about him and where he lived. I then paid for Whitepages Premium to find his address info and called his surviving spouse who, fortunately, responded to my voicemail. Her daughter got involved and found the owner's group password. She helped us get it reset so I could log in as him. I immediately added 2 more owners and that was all we needed. I sent them a popular restaurant gift card for their trouble.
Good luck!
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Jim
Jim Wilson