@Johnny Action , Azure Stack Hub works in a disconnected scenario. If the Stack was deployed connected to Azure, then there is a dependency on Azure AAD. Here is the impact to Azure Stack Hub functionality in connected scenarios if AAD is unavailable,
Portal access both Tenant and Admin would be unavailable, depending on how long AAD is down as would any ARM applications or applications in stack using AAD. A VM would continue running but CRUD operations would not be available and new VM creation would fail. So, the impact is similar to Azure where most capabilities would be restricted/unavailable but the workload itself typically would continue to run.
Note: In a fully air gaped/disconnected deployment against ADFS there would be no impact to the Azure Stack Hub