Is there a lash serum that gives you permanent long lashes that don’t go back to their original state after you stop using it?

Unfortunately there is no product available that will permanently make your eyelashes longer. Your best option is Latisse, but this does require consistent use to maintain the increased length and fullness from the product. 

No there’s no such thing. Of course there are some lash hair loss conditions that are temporary which means the lashes would return anyways. But no, there is absolutely no such product.