They go into a panic. Typically this is called a distablized narc.
Typically this is when they are so desperate for attention they make the biggest mistakes. They are ready to leave their primary supply due to the supply figuring them out or they are losing control.
This is when they actually can get played or hurt.
The narc always has supply but primary supply is needed at all times.
So the narc knows this is happening and does everything in their bag of tricks to keep you hooked or at bay while they frantically try and promote a secondary source.
Once this is accomplished they run and leave you in a world of pain and confusion. This has taken so much energy for the narc. The smear campaign they created while playing you and the other supply.
This is now such a desperation pick they begin to make very bad choices. This is where they get pregnant or married to the new supply within the first few months. They become financially reckless all in the name of control.