I'm going to both agree and disagree with Alex and Iridium here.
Yes, if you care about the device working and not being damaged you should solder this back, no questions asked. Maybe even get a new capacitor, just in case.
If you want to learn something, possibly at the cost of your controller? Leave it off. See how the device fails, if it does. Maybe put an oscilloscope on it to try to figure out why. Which component fails or underperforms? And then you can compare the measurements with a fixed controller, or with a working one. This might damage the device, but it's a good learning moment to just mess around and try stuff. And it would be a crying shame for all those test points on the PCB to go unused...
I'm agreeing with Iridium here, it's far better to solder it back on.
A missing capacitor can mean a lot depending on the application. It could even lead to oscillating behavior that could cause damage to the rest of the device if there is a switching regulator involved, and a capacitor at this high of a capacitance is not inconsequential, big capacitors do big jobs.
The best choice is to solder this 100uF capacitor back on. The controller may appear to function correctly without it, but may have problems under specific conditions such as when the motors activate for vibration.
Thank you all for the help. I'll try to solder it.