Is it permissible for the husband to keep the ticket allowance disbursed for the entire family, or does his wife have a right to it, in the event that he wishes to save the money and not use it for a temporary return?

If the amount paid by the embassy is for outright ownership, then the wife has the right to the value of her ticket from it. However, it is not permissible for her to travel alone without a mahram (definition) (unmarriageable kin), due to the Prophet's ﷺ saying: "It is not lawful for a woman who believes in Allah and the Last Day to travel the distance of a day unless she is accompanied by a mahram." Her right to the money remains, as it is considered a gift to her.