If you delete resonator it will not throw CEL,unless it’s the catalytic your referring to then yes definitely it will throw CEL.
If you remove resonator it will be very loud,I had a Wrx mid pipe and Wrx axle and no resonator I didn’t last 2 hours with it was so annoying and cannot stand the drone when decelerating..so I left the Wrx axle back but reinstalled stock mid pipe and sound much better not annoying at all.