I can’t see any insurance that will schedule a evac flight just for a positive test unless you are paying well into 4 figures for the insurance.
No a positive test result, you are in a medical emergency situation and have a real need for the evac. Many medical and comprehensive travel insurance policies include medivac coverage. For example we buy travel insurance for 6 - 8 month stays out of the US each year, and the medical/medivac coverages are all we are really interested in. We carry coverages of $50,000 medical and $1,000,000 medivac (US) + the typical trip cancellation/delay/interruption coverages for ~$140/couple. Emergency medical coverage for sickness from COVID-19 is included, emergency medivac for COVID-19 sickness depends on the level of care where we are...
Heck even Medicare provides emergency medical coverage outside the US, but it is secondary coverage and that can be a huge out of pocket expense! I don’t know if Medicare will step in to cover costs for major medical, etc. We’ve had friends visiting us have medical emergencies (while traveling) and with one insurance provider it was an excellent experience.