The role of the containment ring is to prevent a detached fan blade from flying straight off. To illustrate the damage potential, recall the DC-6 accident at Burbank where a departed prop blade passed through the fuselage and hydraulic lines before damaging the number 2 engine which failed not long after.
https://aviation-safety.net/database...?id=19760208-0
The errant blade will lose energy contacting the containment ring, possibly more than once, but may gain energy from the remaining fan blades - all within a fraction of a second before it exits the cowl in whichever direction not blocked by the containment ring.