General Antonyms:
* Erasable
* Fading
* Ephemeral
* Fleeting
* Temporary
* Transitory
* Changeable
* Mutable
* Forgettable
More Specific Antonyms (Depending on Context):
* Forgiven (if referring to a stain or mark on one's character)
* Removable (if referring to a physical mark)
* Reversible (if referring to a change or effect)
* Alterable (if referring to a memory or impression)
The best antonym for "indelible" will depend on the specific context in which it is used.