We start the process with gamma rays collision that produces positron electron pair, the pair then annihilates when hit each other and gamma rays are produced again and everything repeats. Sure, in every step we loose energy but can we keep adding energy to keep this process of constant annihilation/creation? just like we can keep oscillations going?
The classical electromagnetic wave is a superposition of zillions of photons in the underlying quantum mechanical framework.
Main stream physics at this time accepts that the underlying level is quantum mechanical. How the classical electromagnetic wave emerges is shown mathematically in this link.
This is the mathematical representation, Feynman diagram, that can be used to calculate the probability of a gamma photon interacting with a field and, given enough energy, generate an electron positron pair.
These two particles cannot meet again to interact as they are going off in different directions.
If the gamma rays impinging on the field have a very high energy , it may be possible that by creating a large number of these pairs, the annihilation gammas can again react with the field and generate more pairs with lower energies. It is a process of diminishing returns, at some point the generated photons from pair annihilation will not have enough energy to give more pairs.
Energy and momentum conservation are absolute laws.