I tried deleting a subnet from my Azure Vnet, but that failed. THen I figured out how to just change the mask length of the subnet, so I don't need to delete it anymore. Problem is, the entire network is now marked as "failed" and I can't do anything to it because of that state.
So, how can I "reset" it to a successful state without deleting it?
Why is your VNET stuck into the failed status?
If the configuration of your VNET are correct, then you can try to follow the steps below to refresh the status of your VNET:
Get the VNET : $vnet = Get-AzureRmVirtualNetwork -Name VNET_Name -ResourceGroupName Resource_Group_Name
Reconfigure the VNET: Set-AzureRmVirtualNetwork -VirtualNetwork $vnet
If the reconfiguration still fails, then please check the configuration of your VNET, correct it and reconfigure it again.