According to Dr. Jones' book sometimes people will stop taking their Urso because their liver function tests have returned to normal. If your liver enzymes have returned to the normal range it just means that the Urso is working. The PBC isn't cured - it is just controlled.
We don't stop taking our BP medicine when our BP is now normal. If for some reason you do need to stop taking it, you just stop it. There is no need to wean yourself off of it.