Have you contacted the county genealogical society in Johnstown,PA?(It's Cambria County,I believe.) The library is another possible source of information. They may have stories about specific families in the area at the time.
Your family may be also listed in the city directories, and census material.

Also, Ancestry.com has reference material:
"The story of Johnstown : its early settlement, rise and progress, industrial growth, and appalling flood on May 31st, 1889"

Hope this helps you find what you are looking for. (My grandfather and great-grandfather were among those searching for survivors for more than a week.)