Any ideas of how to fall safely off hydrofoil?

[Russky]

Every time I fall from a foil board at full speed I pretty much pray for the least possible damage .

The point is to send it as far as possible, in, preferably, opposite direction.
Unfortunately, at those speeds, foil boards, when let go, tend to travel as they wish, usually exactly to the point where you are going to be... just my experience ...
It's pretty amazing, even when they jump with the foil and drop it in midair - it will end up exactly where you are going to touch water ...

After getting a "boxer" scar on my eyebrow, it is 100% helmet/impact vest/shatterproof glasses (for foiling) for me.
When crashing, try minimize possible damage - if you can, cover you head/face with your arms, tuck your feet in, etc.
Also, when crashing at speed, try to "duck" the board's nose into the water - it will stop and stay stationary that way.