SASless
I presume you refer to the US where most HEMS are loss making projects funded by hospitals to pull in very profitable major surgery. That works well but in the UK we have socialised medicine. There is no profit. A large operation such as a heart transplant is a big COST or loss for the hospital not a profit. Hospitals do not get paid for treating patients, they have to pay the costs themselves or via the CCG
SilsoeSid
There is no problem with return to base or return to hangar at night and London HEMS have done the latter. This dubious project is about flying to trauma sites at night, and not just city centres where in Essex you might be able to manage with half a dozen recycled sites per city - although why you would do so is beyond me as you would have to task land transportation to collect the crew and then a land ambulance to transfer the patient and after all that nonsense you could have the patient in the operating theatre much sooner and cheaper and safer in a land vehicle.
No this is about going to night trauma which is often down country lanes with little ambient lighting, trees, livestock, inclines, farm implements and cables and wires. You have to land within say 50 metres as there is no spare personnel to transfer you to the patient and you will have to manhandle the patient plus stretcher plus monitoring plus oxygen to the aircraft so no hills, mud or cow pats please. I would be interested to know how the military would approach it.