For many would-be Stalins, the main point isn't the torture, but the kidnapping and incommunicado imprisonment (eg. in gulags).

The utility of torture comes in when you want to ensure the prisoner's compliance when reintroduced to society.

So: please note that immortality by itself doesn't preclude either sequestration nor adversarial behavior modification.

Technical solutions to both of those (integrity checks to detect coercion, restoring from distributed backups, etc.), start to run into the same sort of arms-races we have with internet filtering, botnets, and malware. Except that so far as a totalitarian regime is concerned, the uploaded dissident is the malware, as is any sufficiently advanced freedom-preserving tech.