You can set Oberlo auto-update settings to unpublish such product whenever the item runs out of stock - as such you won't sell out of stock variant. To do that, just go to Oberlo > Settings > Shop Settings > Auto updates
We will run few more syncs then and if that product still doesn't appear on AliExpress we will remove it.
You can remove such product from Oberlo as well.
Hope this helps!
Just drop me a line if there's anything else I can assist you with.