From my experience exiting your ship in atmosphere is purely limited by game mechanics and theres a smart system in place that prevents any accidental deaths. You're only able to exit once properly landed or when the auto landing sequence kicks in really close to the ground, so no need to worry about fall damage or sudden deaths. The game completely blocks mid flight exits which is honestly a clever design choice

Something worth noting is that while you cant fall to your death, environmental hazards are the real threat when landing in dangerous areas. When you step out your exosuit protection starts ticking down if youre in toxic rain, extreme heat, or other harsh conditions, so always check the planets conditions before popping out. Its actually a good idea to keep an eye on those hazard readings in the bottom corner, since theyll tell you exactly what youre dealing with before you even open the cockpit

Your best approach is to scout safe landing zones when possible, and if you do need to land in hazardous areas, make sure youve got enough protection modules charged up first. The game wont let you accidentally eject yourself mid flight but it will let you walk straight into acid rain if youre not paying attention to those environmental warnings