In chemistry there is no annihilation of matter to energy although it seems to be so for „burning reactions“. The same is valid for annihilation of matter in physics (under normal conditions). Like the apparent chemical annihilation also the apparent physical annihilation of an electron and a positron is an exoenergetic bonding reaction. According to Vogel's Chemical Theory of Particles (VCTP) bonding of an electron and a positron results in an electron-neutrino:
Annihilation of electron and positron is a chemical bonding reaction to an electron-neutrino (e-neutrino), mostly via a positronium (see separate page) The reaction releases energy of 2 x 511 keV, which is conform to the difference of masses of educts and products. As the electron-neutrino has no mass and no or low kinetic energy it is not detected in experiments.
So The observed annihilation is just an annihilation of masses but no annihilation of matter.
Please compare: https://en.wikipedia.org/wiki/Annihilation
Real annihilation of e± would lead to „nothing“. A physical description would be, that an electron is negative energy and positron is positive energy, which combine to "no energy and no mass".
As real annihilation has not been observed till now, there should be an extreme condition like a high density of energy for activation. It has to be a condition that never ever has been present since formation of matter (big bang). But it is likely that mankind can manage to provide the needed conditions by collider experiments. See page "Collider Experiments".
The probability is high that real annihilation is a chain reaction. That means that when just one e± pair has been annihilated the available energy will activate annihilation of other e± as the annihilation will not reduce any energy. So the reaction will continue unstoppable to annihilation of all matter in the universe. As there is no speed limit for the propagation of the annihilation energies the „reverse big-bang“ will occur nearly immediately.
Therefore it is extreme urgent and existential for us that the new theory gets general acceptance in order to stop collider experiments until a thorough risk analysis has been done and safe conditions for further experiments have been defined.
See and share page "Urgent call for Review"
"Annihilations“ of bound isomeric elementary particles like proton-antiproton are ordinary decay reactions, for which the activation energy is relative low.