Vincent wasn't 'saving anything' for the return trip, so I think the idea the movie was trying for was that he would be able to do the mission but wouldn't live to return whereas a non-degenerate would eventually make it back alive.
Of course reality is he's already past his life expectancy and he's putting the mission at great risk entirely for his own selfishness, but you're not supposed to think about that.
I've always wondered why there wasn't a sequel. 5 minutes long where vincent has a heart attack upon entering orbit and the mission is a failure.
Vincent wasn't 'saving anything' for the return trip, so I think the idea the movie was trying for was that he would be able to do the mission but wouldn't live to return whereas a non-degenerate would eventually make it back alive.
Of course reality is he's already past his life expectancy and he's putting the mission at great risk entirely for his own selfishness, but you're not supposed to think about that.