The 62-year-old actor, who only had one day left of filming before Paul died in a car crash on 30 November, was speaking at the Sundance Film Festival where he was promoting a baseball documentary.
"[Paul] was a terrific guy," Kurt told Associated Press. "They're having to rewrite, they're having to do whatever they're having to do to deal with the situation.
"Listen, it's catastrophic. It's the worst thing that could happen to a movie, but it's not as bad as what happened to Paul. Life is full of curveballs."
Kurt, who joined the action-film franchise to play a "father-figure" to Vin Diesel's character, added that he didn't know what the script-writers were planning for his character.
"I don't know what is going to happen," said Kurt. "It's obviously a difficult situation. Whether or not this guy dies off in the movie, we don't know. That may have changed now significantly too."
The actor, who has been in a relationship with Goldie Hawn for more than 30 years, said that he would return to set some time this year. Filming for Fast & Furious 7 was delayed after Paul's death and the release date was pushed back to April 2015.
Goldie Hawn and Kurt Russell
In early January, reports emerged that Paul's younger brother Cody had been asked to step in to film his late brother's final scenes.
"Producers had a string of meetings right after Paul's death," a source close to production told the Daily Mail. "They soon realised they needed someone who looked like Paul to finish the movie, and that's when they approached his early identical brother Cody.
"They can shoot Cody from behind and at a distance, and if it's a shot they need Paul's face in close up, they can CGI it later on. If Cody agrees it's because he wants to honour his brother's memory. There are many details that still need to be worked out, but right now the family and cast and crew are still grieving."