Bones are strong in compression but weak to rotation. See this extremely useful and easy to understand youtube channel for more details on that:
I’ve bailed off at 20+ mph and was fine aside from my dignity. Went by a construction site that hadn’t seen work in months, thought the sounds were coming from my board, bailed without making any attempt to slow down first to prevent any further damage to my board if something had broken. I managed a good two or three steps at 21mph before my center of gravity was too far forward and I slide in the tiny strip of grass next to the road.
Bailing off shouldn’t pose any risk of broken ankles so long as you have practiced it before hand, and even without practice you’d need to really fuck up your footing to risk any breaks.
Most of my falls were from riding in wet conditions, but I have had two bad falls as a result of things out of my control. First was a newly “finished” bridge with a giant fucking gap without pavement that I couldn’t see before hand and I had a car on my ass so once I did see it a second before I hit it I couldn’t slow down without risking getting hit. Stopped my board the second the wheel hit it and launched it several feet away from me while I kept going straight and hit pavement hard.
Fucked up my PCL with a minor tear (so no surgery needed) and the cushion in my left knee was destroyed. Still hasn’t fully healed and that was back at the beginning of June, but the PCL tear does have a healing time of 9 months 
I could and can still use my knee without issues thanks to the , but I can still feel that it is a bit off. Also unlike the ACL, when you damage the PCL you still have your complete range of motion. Only thing I had to avoid was putting too much weight on just the left leg while standing still since my knee would hyper extend which puts unneeded strain on the PCL while it is trying to heal.
The second one that was 0% my fault is already detailed out here: Catastrophic Surf Adapter Failure
I think the only thing not mentioned there is the internal injury I received from the fall from coming to such an abrupt stop with little to no sliding at all. The symptoms weren’t bad enough to need a hospital visit and if I went they’d just tell me to watch my torso and rest anyway.
I will not comment on protective gear since I do not use anything other than a helmet. Don’t do what I do if you like having skin stay on your body. I am an idiot I take known risks by not wearing gear. knee pads and elbow pads would likely get in my way more often than they’d help me which is why I don’t use them. The only real time I wish I had them was the part failure since they might have let me slide more after the fall and I wouldn’t have been stuck in bed for a week straight in extreme pain. All my other falls they would have just saved me from having to treat and bandage burns.
My highest capable speed right now is only 25-26 mph and that is if I want to drain my battery. Normally it tops out at 21mph. If I was going to push it up to 30mph then I’d likely buy some gear and use it anytime I planned to go that fast.
Before riding, look up your local orthopedic doctors and do some research to see if they offer same day emergency visits. If you do break something, then you do not need the ER and even if you went to the ER they’d call in an orthopedic doctor anyway and charge you 2-10x as much.
I may have written too much so TLDR:
DON’T RIDE IN WET/ SLIPPERY CONDITIONS IF YOU LIKE YOUR SKIN
KNOW HOW YOUR PARTS ARE SUPPOSED TO WORK SO YOU DON’T USE A DEFECTIVE PART FOR OVER 2000 MILES
INTERNAL INJURIES FUCKING SUCK
BONES ARE STRONG IN COMPRESSION BUT WEAK IN ROTATION