I used to be a Gurston regular but have to qualify this reply by stating that I haven't been for the last 3 years.
I recall that a small spectator area is/was level with the curve at Hollow but situated well back by hillclimb standards. Thereafter the spectators have to climb up and away from the track into trees to reach the main viewing area halfway up the hill. I have seen cars crash into the foot of these trees having got Hollow wrong but none have ever come anywhere near the spectator path which by then is a long way above the track.
If that is the area of concern then I would suggest that no track or hillclimb I have ever seen is safe.
No. The path is not an issue. A car going off on the outside of Hollow can do a very, very long "wall of death" after the slip road on the right, bounce in the air and, hopefully, come down again (as I witnessed Tony Marsh, the track's consultant designer, do when I was leaning on the rail feet from the track in the spectator enclosure before Karussel at its furthest point back towards Hollow). Speeds are so high there a winged car could just as easily fly as land. There are bushes at that end that tend to conceal any direct line of sight to the critical point a car could launch into the air, so it is not an obvious risk to the casual observer.
I agree no track is totally safe. I once helped at Wiscombe judge whether the inside bank immediately before Martini should be raised. We concluded - by standing in potential harm's way - that it was not necessary, either to protect spectators at the furthest point of the enclosure, or to prevent cars launching. Years later Rob Turnbull did just that...
The worry at Gurston is the speed at the end of the downhill bit. Even saloons trap at Hollow at nearly 100mph. Big single seaters are at, what? 130mph?
I've done Wiscombe downhill on the RAC Rally but Harewood's only been used uphill on those RACs I've done, as has Loton. I can't see downhill being realistic on safety grounds for open wheel cars from speed alone.