The credits are temporary insofar as other automakers are starting to make their own EVs. How is Tesla going to make a profit when nobody needs to buy its ZEV credits?
They have non traditional approaches to some things, and in that regard they might be able to build EV cars more cheaply than competitors, and it probably also helps that they have lots of experience now, but eventually the fact that the cars are electric won't be the killer feature any more.
Tesla sold about a half of a million cars last year. Nissan sells about 3 times that figure in the US alone. Toyota sells about 18 times that figure globally. Without being too presumptive, it certainly seems like Tesla is not going to imminently stop building factories.