Disclaimer: This is not permission to try this! These remarks are addressed to professional pilots!
In my experience, a lot depends on the machine. The 206 family is probably the best machine for low-level autos, in terms of high inertia blades and crashability - not all machines have both!
When I did power line survey, we taught the guys just to take what was below - if they were very slow and low, a slight check back on the cyclic, DUMP THE COLLECTIVE and haul it in very quickly at the bottom (there's a great article about this by Dennis Venturi (no relation, I'm sure) in Helicopters Magazine some years ago (in Canada). Briefly he points out that if you do a quick pullup on an aerofoil you will generate a vortex across the top surface keeps the boundary layer to it and you will be able to go beyond the static stall for a second or two - possibly generating double the lift. Look for dynamic stall at NASA AMES as well for more info. The jettie will do a vertical from 50-75 feet BUT - as Shawn Coyle pointed out in another post some time ago - that was a test situation - in a real engine failure at that height (and arguably at any lowish height) you would likely be on the ground before you realised what was going on if you are not paying attention.
I would always try to do a vertical, even at the top of the H/V curve, which is 400 feet in the 206. But that's my personal choice, knowing the machine as I do.
If you had some speed on, cyclic right back, zoom climb and see what's below - the Gazelle does this admirably. Again, it depends on the machine.
The operator should be determining the safe routes in the first instance. In a valley as in Scenario 1? You would have to perform a controlled crash - also look for a US Army document called how to crash a helicopter.
Tin helmet is now on....
Phil