*Spoiler warning* (Taken inspiration from the arasaka ending)
After completing the story, V learns that it is inevitable that he/she consciousness will die. Romanced character/fixer, learns the location of an imprisoned medical expert who was studying the process of cloning using black market tech.
V either by themselves or chosen alliance raids the prison/facility the doctor is being kept at (the reason he was never mentioned by arasaka in the story was due to non one believing in the process of his work being “legitimate” and or possible.
There would be multiple endings to this dlc but the two primary ones are related to V and Johnny.
*Good ending*
V dies the same way Johnny did (through soul killer) his/her mind is transported onto a biochip and after some time the scientist who we saved during the dlc replicates Vs body as a clone and allows it to host their biochip ( basically giving V a new non dying body). The difference between this ending and the bad ending is that during a seperate raid on an arasaka facility during this dlc, V learns that Johnny’s consciousness was not just limited to the original relic, the bad ending is choosing not to do anything with such information, the good however is the dlc ending and sometime after your character was resurrected the scientist informs you that he performed the same procedure on Johnny, Bringing him back to life (a clone body as his host)
There would be heaps of interactions you two could have based on the story leading up to this point, but this dlc would allow for the game to end with Johnny becoming the king of the afterlife as V would have if they chose that ending, and getting back with rogue, whilst V decides to settle down/ leave night city with their romance choice.
This dlc could either happen before or after the games ending because it would make for a good ending seeing Johnny finally getting his revenge on smasher and getting back to rogue without her dying.