Yes. You can subpoena in a lawsuit. An experienced attorney might be able to get pre litigation

The location not matter if the store controls the area of the fall.

In some states, once the person dies, there is no longer a personal injury lawsuit. Consult with experienced attorneys.

It is possible depending on factors as to notice, why pipe broke and or the surface of the floor. Consult with experienced attorneys.

Personal injury and or housing who specializes in mold.

This is probably a discretionary act of the city for which a lawsuit would not lie. Consult with experienced attorneys.

A lawsuit is possible. Consult with experienced attorneys. Use the Avvo search tool to find an attorney. https://www.avvo.com/find-a-lawyer

The police may determine who to believe. You can submit your story to the DA.

They have a right to view things open to the public.

A lawsuit is possible. Likely expensive. Consult with experienced attorneys.