Maintaining the EHCP is evidence based, and with the state of finding being what it is the local authority would be happy to cease the plan.
At the next review you need to present evidence that the plan is no longer needed. This would essentially be that the outcomes in the plan have been met, and that there are no further outcomes related to the child’s SEN to set.
If the school disagrees that the outcomes have been met, they’ll need to provide evidence for these ongoing needs.
In this case your evidence might need to come from outside school eg from a paediatrician, speech therapist, occupational therapist depending on the nature of the needs.