Is a disc extrusion c/3/c4 that's gone from small to large in a year and a half and indenting cord eventually going to need surgical intervention?

Yes: The major driver for the timing of surgery are signs/symptoms of nerve damage in combination with your level of function and pain.These symptoms include numbness, Tingling, muscle weakness such as decreased grip strength and Muscle Atrophy. An EMG can evaluate the extent of nerve involvement. Physical Therapy can help with symptoms and function. Surgery can remove the extruded disk relatively easily