Let's say I crashed and broke the camera, gimbal, and landing gear...

[Elektrik-Eye]

- could I replace the camera assembly and legs and be good to go, or are there internals/calibration that has to be factory-performed?

Asking for a friend.

 

[msinger]

could I replace the camera assembly and legs and be good to go

If you're sure that's all that's broken, then, yes, you could just replace those items.

are there internals/calibration that has to be factory-performed

No. Your friend can perform any needed calibrations via DJI GO or the DJI Assistant 2 application. If anything, an IMU calibration might be a good idea since the drone crashed.