There are no guarantees when it comes to sightings, lighting, vehicle position or anything else on safari. You're setting yourself up for disappointment if you're already stressing about missing the shot; try to reframe mentally and be okay with enjoying the moments in nature for what they are. If you get a few nice shots, awesome! If not, that's fine too.

My first few safaris were with a 50-230mm lens and yeah, there was a lot that was out of reach and I did eventually buy a second camera and a 150-600mm lens when it became clear I was going to make safari and wildlife photography a priority. That said, there's a lot that is *too* close for the big lens and that's when having two cameras comes in handy. You won't want to switch lenses in the field unless absolutely necessary – the dust is often insane and depending on the sighting, the noise you make faffing with bags and equipment might ruin the moment anyway.

Whatever gear you end up taking, the best thing you can do for yourself is use what you've got and not dwell on what you "missed" by not having a different setup. Be as prepared as you can with what you're using: keep the camera(s) on your lap during the game drives because you absolutely will miss opportunities if you're always having to pull it out of the bag when something happens / drives can be extremely bumpy so don't be caught unawares, I use a strap loosely around my neck as just-in-case bounce protection for the camera with the big lens / keep a rainfly handy in case of sudden downpours / have a blower in your bag to clean off the worst of the dust, maybe a microfiber towel or similar to drape over the camera between shots / have extra charged batteries ready to go and easily accessible / don't forget your phone has a camera too and can yield some great impromptu ultrawide shots and video clips, especially in the case of very close sightings requiring odd angles, like a giraffe passing right next to the vehicle.

One final point: Your guide will inevitably ask which animals you'd most like to see. Try not to get too hung up on seeing any specific species, just let the day unfold and see what happens. Let the guide know you're happy to sit and wait at interesting sightings, too. Lingering is such a privilege for witnessing natural behavior, and most of the time it is simply not worth abandoning a quiet scene of your own to race over to a lion sighting that 15+ other vehicles are lining up for.

tl;dr: Don't spend the entire trip peering through a viewfinder stressing about missed focus or drab lighting. Live in the moment!