No country will have their nuclear attack submarine go and rescue a target period.
Geneva Convention (II) 1949
Article 18 - Search for casualties after an engagement
After each engagement, Parties to the conflict
shall,
without delay, take
all possible measures to search for and collect the
shipwrecked, wounded and sick, to protect them against pillage and ill-treatment, to ensure their adequate care, and to search for the dead and prevent their being despoiled.
Whenever circumstances permit, the Parties to the conflict shall conclude local arrangements for the removal of the wounded and sick by sea from a besieged or encircled area and for the passage of medical and religious personnel and equipment on their way to that area.
1982 UNCLOS
Article 98 Duty to render assistance
Para 1. Every State
shall require the master of a ship flying its flag, in so far as he can do so without serious danger to the ship, the crew or the passengers:
(a) to render assistance to any person found at sea in danger of being lost;
(...)
Lethality of current commander in chief is his own problem; conduct of US skipper - supported by DoW, -
does constitute a breach of (1)law of the sea, (2)International Humanitarian Law obligations, and Law of war at sea.
US is signed under 1st document, and while UNCLOS isn't ratified by US, they, quote "treat it as a source of common law".
Remarks:
-shall in legal writing is a binding verb, used when necessary action is higher than "must";
-without delay - means, as soon as engagement is finished. Since "each" is used before it, possibility of other standing orders is not excuse of breach of basic humanitarian requirements, unless engagement continues.
-all possible, unlike "reasonable", specify urgency of full rerscue action. This is specified duty, not choice.