Safari Decision... leave the Oly 40-150 Pro behind?

Chizuka: I've been on dozens of safaris, and I strongly disagree with everyone who's advising you to leave the 40-150 behind.
What lenses you keep mounted on your two bodies would depend on the time of day and weather conditions.
Drives typically start early mornings and end a little before noon, when the sun is getting high up. Evening drives start in bright light but end at dusk (or well after sunset).
When the light is bright, you'd want to keep the 100-400mm on your Panny (better image stabilization) and the 12-40 on your OM-D (I apologize if I got some details wrong - recalling your original post from memory).
Yes, it's a good idea to have 2 bodies to avoid changing lenses in the field. However, it's equally true that there will be stretches of time when nothing's happening. This will give you plenty of time to switch lenses, as the light conditions change.
In early mornings / late evenings, you'll want to have the Olympus on. And yes, you'll get better reach with the 1.4x teleconverter ... BUT: you will regret not having that extra stop of light when the sun isn't shining brightly.
People worry too much about having as much reach as possible. It's wonderful to take detailed portraits of lions, or oxpeckers on a buffalo, or an elephant's skin. But you know what? It gets old. You don't want your photos to come out looking like they were taken at a zoo, do you?
So it's very important that you take photos that show animals in their habitats. Trees + elephants give a sense of scale. Same with leopards + branches. Or cheetahs + savannah. You get the idea.
When light is low, if you have the 1.4x TC on, your photos will get blurry. Or very grainy. I am speaking from experience. When animals are moving, and your vehicle is trying to keep up, the shaking and movement will affect photos. They'll look fine on the LCD, but when you see them on the computer, they'll look blurry.
You'll get plenty of opportunities for reach & bird photography in bright light. In low light, use the Olympus.
And since you'll go on multiple drives, you could take some pics with the 1.4 TC, and some without. You'll get a better feel for what's working best after one or two drives, so don't worry too much about it.
As for me: after losing many good opportunities with the Olympus 40-150 f4-5.6, I began using bright, manual focus lenses more (this was before Pro lenses / Panny 100-400 were available). And despite manual focus, my keeper rate improved dramatically.
I now use a Canon FD 300mm f2.8 quite a lot - with & without TCs. I am not asking you to use heavy, manual-focus lenses. I am advising you not to ignore the importance of having a BRIGHT lens, versus only thinking about reach.
You can take beautiful photos without extreme focal length. In fact, you can take better photos that way. You can't fix a blurry or grainy photo that's nothing like what you saw in real life.
Good luck on your safari! I hope you have fun!