What happens if someone has hpv which goes away before she has a smear test, but then it resurfaces afterwards? could this keep happening and the virus be missed?

The Pap smear was used for decades to pick up & treat early signs of pre-cancer/cancer before the link to various HPV strains were known. Whether or not you test + for high risk strains you will still need screening. Testing + may push screening to be more frequent. You can test + for high risk for a lifetime and never develop a genital cancer.