Tifa being dead makes no sense at all.

Cloud's confabulation is the direct result of meeting Tifa, because Tifa has Tifa's memories and his shame subconsciously caused the JENOVA-S-cells to awake so he read her memories and suppressed the part of himself that knew what was true to match Tifa's memories. "Doris" does not have Tifa's memories. It would have to be written different.

The basic idea is not bad.