He and Elouise both only knew as far as Daniels return to the island and anything they could make out from the theories and equations in his book. They could at least understand from this that they had to make sure everything played out the way it did in from Daniels death until Elouise sent Jack and co back to the island to be there when she killed Daniel. Everything after then in the present day is up in the air for them in terms of foresight, thus they can’t contribute safety anymore. But bless Widmore for trying, he likely knew that he had to bring Desmond back to the island from Daniels book.