No other details are available at this time.
Storms left temporarily in 2011 due to illness. The role was taken over by Jen Lilley. Later it was announced that the leave was permanent.
It's possible that at the time it was announced that Storms would not be returning to GH, producers, as well as Storms, believed the show was wrapping up. With the extension, she has now had sufficient time to recover.
Maxie has been through an awful lot since Storms left - her murder confession, jail time, marriage, and her mother returning -- but we have no doubt that she can resume her role very easily. If she does returns, her many fans will be thrilled to see her.