I discoverd this last night.
Here are some basic rules of gantz.
1. When you die you are copied and sent to gantz (if he chooses you.)
2. When you choose to revive someone from the memory they either come back to Gantz or have their memory wiped.
3. When you choos to be free your memory is wiped.
Now on to the Titz Theory Basics
1. Somdthing went wrong when titz was transfered to gantz. Their is another version of her out there.
2. Titz is the copy and her origial managed to servive. (I beleave this is because after she slit her wrist Gantz sent the copy. Then her mother walked into the bathroom and called 911. The origional servived. Seen in Volume 2 and later on)
3. If Kei revives Titz she will either be sent back to gantz or have her memory wiped.
4. Since her origional is still alive she can't be sent back to her normal life. cause the origionl will notice.
Now in order to revive titz-copy Kei would have to kill Titz-origional. But this is pointless because of one simple fact.
Once Titz copy is set free. She'll forget all about Kei. So Kei should just not bother to waist his time on Titz-copy and just find a way to introduce himself to Titz-origional. Either way In the end Titz-either won't remember him and vise-versa.
So the outcome. Save your 100 pointz and get the damn weopen!