Tearing an antenna usually degrades its RF performance, your cellular reception will still work but with degraded performance, like maybe slower speed, no service in weak coverage areas, higher power consumption.
The right antenna also serves as the proximity sensor, if it is torn, the cellular module will not properly regulate RF transmit power when your hand is touching the area. So the transmit power may be over safety limit(in my opinion not a problem, the whole idea of cellular signal causes cancer is bullsh1t) or constantly latched to low power setting due to the sensor falsely triggering. This can cause performance issues.
So if you think it is a problem, replace it.