Does it become permissible to travel if a mahram is present for the departure, with the possibility of his absence for the return?

Islamic law stipulates the presence of a mahram for a woman's travel. If this condition is met, she is permitted to travel. The matter does not depend on guaranteeing her return with him. If her return with him becomes impossible, and there is a necessity for her to travel without a mahram, then it is permissible for her.