The IMA battery can be completely removed from the car, and the car will still function, if the DC/Dc converter can have the HV input it requires.
The typical way to do this is to remove the whole connector/relay board from the pack, and use it to make those connections.
If the fuse and connector from a used pack is available, a much safer and simpler IMA bypass can be construced.
You remove the DC/DC connector, the 30A fuse, and make up some wires with ring terminals, and make a short bypass connector with those components. It is important to keep everything well insulated, and prevent ant possible shorts, so here is how I made mine.
If you can leave the HV battery in the car, just pull the "A" connector of the BCM and turn off the HV battery switch
location of BCM A connector