Wow, what an adventure. I love downwinding on foil, the silent carving....but 120km is about 110km more than I'd be comfortable with at this point.
I am still low-level intermediate, and find it is quite tiring on legs compared to surfboard. Joint pain alone would end it for me.
Also find it interesting to control speed when downwinding.....if overpowered get going too fast, but if underpowered the kite can't drift fast enough and may backstall (and I have the best drifting wave kites out there). I bet you had some active kite flying to keep things working right.
Around here, bull kelp is the enemy. Big patches are easy to see, but a few lone strands can hide under the water, especially when visibility is poor. A quick stop and unplanned eject results.
That is scary story about missing knife....no joke, wrapped in net, things going sour from there, that could be how you die. <shudder> I keep hearing the same story from buddies, when the S**T hits the fan, "oops, forgot my knife / it fell out / blade rusted out". Call me a safety nerd, but I'd have 2 knives on a trip like this, one in harness, one mounted somewhere in reach of your head/neck/shoulders, for if you're too wrapped up to reach your harness.
Next trip: find a GPS watch! That would be an awesome track to have recorded.