You can probably fly it blind with no camera attached and then literally stick a gopro on the bottom.
There are gimbal systems for the gopro can be used - this was the way it was done with Phantom 2 and earlier.
Seeing a live image from the gopro is where it gets difficult and expensive, plus you won't get most (or any) of the additional data which is a major part of why the P4 is so easy to fly. 

The camera can be replaced but it's probably beyond the average user to do it themselves. 
There's a healthy market for damaged drones - some will repair them, some break tem up to repair others -  or sell the good parts separately yourself like the controller and batteries and put proceeds towards a new one?

I would say get what you can salvage and buy another.