Usually yes, and the specifics vary more than people expect. Many expedition operators require medical evacuation and repatriation cover as a condition of travel, while others publish a strong recommendation or include a limited assistance arrangement. Never assume the requirement is the same across companies. Ask your operator for the exact written minimum, the required wording, the geographic scope and the proof deadline, and do it before final payment rather than shortly before you sail.
South Georgia builds insurance into its Entry Permit. You have to confirm cover for emergency evacuation for anything that can't be treated in the territory, transport and medical care in transit to the nearest country with suitable treatment, and repatriation of mortal remains.
The Falklands visitor permit page states aero-medical evacuation cover of at least the equivalent of US$2,000,000.
Operators typically want a certificate showing your name, insurer, policy number, a 24-hour emergency number, dates, coverage amounts and the evacuation and repatriation benefits. Carry it digitally and on paper, and keep the full policy wording accessible, because a summary often won't show the exclusions.