In Malaysia once tested positive you're admitted to a hospital for both quarantine and treatment purposes. I believe treatment is targeted at symptoms to alleviate them, since there's no real cure for COVID19. Patients are released from hospital I believe after testing negative for COVID19 in three successive tests.
As with most infections, recovery is usually accompanied by immunity, however in some viral infections like dengue, immunity from one sub-type is actually a prerequisite to a more severe reaction if the same individual is infected with another sub-type (there are four dengue sub-types). So far there's been no evidence to suggest that COVID19 exists in several distinct sub-types as far as I know, but if it were to be the case, this pandemic is far from over.