this is the limit included with the hub cost:
but that 84 GB sounds like what is included in hub cost. it can keep going until the storage handles: https://learn.microsoft.com/en-us/azure/storage/blobs/scalability-targets
You will probably see that error from the hub side, therefore:
"Event Hubs emits exhaustive metrics that provide the state of your resources to Azure Monitor. They also let you assess the overall health of the Event Hubs service not only at the namespace level but also at the entity level. Learn about what monitoring is offered for Azure Event Hubs."
this info may be useful: https://learn.microsoft.com/en-us/azure/event-hubs/event-hubs-faq#can-i-scale-updown-my-cluster