I find Mr. Collins saying that Mr Bennet's death might "not be for several years" ridiculous and in very poor taste. After all, Mr Bennet is at my guess in his late forties (he has been married twenty-five years and I assume he was a youngish man when he married). Therefore it seems ridiculous to talk of his maybe living for several years ("It is a miracle his life has extended thus far!" ;-) ). Also, of course, it sounds as if Mr Collins has calculated how many years it might be until he comes into Longborne.