The description of the spell says specifically that after the caster has maintained it's concentration for an hour, the spell can be dispelled.
The transformation lasts for the duration, or until the target drops to 0 hit points or dies. If you concentrate on this spell for the full duration, the spell lasts until it is dispelled.
In another question it was specified that spells which can be dispelled, will last until its effect ends. While spells which requires concentration, will end upon death. However it does not specify what happens with a spell that initially requires concentration.
If the caster dies after this duration, what happens to the target?
- Does the target retain its current form?
- Does the target revert back to the previous form?