From the schematic:
R9 is a 47K pulldown resistor from BOOT0 to GND. It sounds important. I wouldn't trust it to reliably not float. It might work today, but temperature and humidity are going to be your enemy. If this is in your studio, I would just risk it, but if you want to take this unit on the road, I recommend fixing it.
Here is a video for soldering a resistor:
If you're hesitant, you can buy circuit boards to practice soldering. I think you can pick it up in less than 10 tries. You can find SMT Practice Kits very cheaply. It is very intimidating at first, but you can fix your board in less than an afternoon of training.
One of my favorite SMT tools is SMT No Tack Flux No Tack Flux. This will be messy, so it's not recommended on this board, but if you have the time and money, try it on a practice board. It makes a stressful experience really sloppily, easy. You have to clean it with 99% IPA or distilled water, but it's a great help with SMT soldering.