Fischer did not play competitive chess after his world championship victory, making many wonder if he would be prepared to defend his title against Karpov.
Fischer attempted to negotiate a long match supposedly so that he could "sacrifice" the first few games to play himself back into shape. Would this have worked?
We now have a possible answer of yes: Reports are that Magnus Carlsen took a 5-month chess vacation after the Tata Steel tournament in January until the Tal Memorial in June. His rustiness clearly showed in the early rounds of Tal, but he was able to regain form sufficiently to win the very strong tournament (ahead of, for example, Kramnik and Aronian, who played a friendly match to keep their skills up).
So, 40 years in retrospect, Karpov and the Soviets should have acceded to Fischer's demands. It would have been a great match.