South African President P.W. Botha said Thursday that African National Congress leader Nelson Mandela may not have to return to prison from the hospital where he is being treated for tuberculosis. Botha said Mandela had been cooperating with the government, and he now expects "positive results" from his standing offer to free the 70-year-old black leader in return for renunciation of violence. In his speech to the provincial National Party congress in Natal, Botha did not explain what he meant by cooperation.