Regardless of rules, if a boat goes over behind me I slow until I see the crew floating, not trapped, and making progress toward getting onto the hull to right the boat. If a boat ahead of me flips I will slow and hail. I want to know that again the crew is clear of the boat, not trapped. If I see a breakdown, broken rudder gear or mast down I will stop and render assistance or at least offer. If nothing else I can make a radio call for the disabled boat. I am thinking mostly about distance racing here.
On buoy courses I need to rethink my reliance on the crash boat responding. Now that I think of it for the most part they haven't responded. Again, I want to see that the crew is safe then they're on their own unless they need further help in some way and the crash boat is unavailable or off daydreaming somewhere.
I've wondered, what if somebody really needs assistance. I'm a single hander and I guess I would just have to abandone my boat to go help. It can be easily replaced or repaired, unlike my fellow sailors.