Q: Is there a way for "find my iPhone" to work if the app reads that the lost phone is "offline" ?

No.

Okay, But can I know Why it says that device is offline.

Is it because the battery died or what?

Could be a lot of things: the battery died, location services and/or Find My iPhone was turned off in settings, it was restored as a new device erasing all conent and settings, etc.

how would the phone be able to be erased o/restored and how would one get to seetings if a password is required?

By forcing it into recovery mode.

another question please.  is the location of a iphone driven off the sim card only? Meaning what if the sim card is removed, and replaced with another, can the iphone device itself still be tracked once turned on or charged?

It will work with any data connection to the internet, using any sim card (as long as it has a data plan) or wifi.

> No.

Wrong.

I am currently tracking a family member's iPhone during travel. Was working fine in Find My iPhone within iCloud.com. Then, it stopped responding, showing as "Offline". However, using Find My Friends on another iPhone clearly shows the current location.

I don't know why it's no longer responding in iCloud.com Find My iPhone, but it is showing the correct location when pinged from Find My Friends.