The experience that Erica mentions is actually very rare. The ring may be expelled accidentally from the vagina if, for example, it has not been inserted properly, during the removal of a tampon, during sexual intercourse, in conjunction with constipation or in the case of uterine prolapse. If any of these cases apply to you, you should regularly check that the ring is still in your vagina.
In the case where it remains outside the vagina for less than 3 hours, once repositioned in the correct position, the ring will still continue to protect. Thus, you can rinse it in cold or warm water (not hot water) and reinsert it. If, however, the ring has been out of the vagina for more than 3 hours, contraceptive efficacy is not guaranteed. In this case, contact your gynecologist.