Do elementary particles last forever? I have heard that not even black holes last forever, because of Hawking radiation. But what about elementary particles? Will an electron, for example, exist for all time?
 A: Both the proton and the electron, if left alone, will live forever because there is nothing lighter in mass for either of them to spontaneously decay into without violating any conservation laws.
A: Even the so-called stable elementary particles might not last forever,
when there are other particles around.
Take for example electrons:

*

*Electron-positron annihilation:
The electron may be hit by a positron, both disappear, and 2 photons will appear.
$$e^- + e^+ \to \gamma + \gamma$$

*Electron capture:
The electron may be captured by a proton (from a proton-rich radioactive nucleus),
thus giving a neutron and a neutrino.
$$p + e^- \to n + \nu_e$$
A: Hawking radiation is theoretical and conservation laws are still obeyed. Electromagnetic radiation is released, and conversely the mass of the black hole decreases due to quantum mechanical effects. Elementary particles can decay into other particles or electromagnetic radiation. https://en.wikipedia.org/wiki/Particle_decay
A: The electron, an elementary particle, is the least massive carrier of negative EM charge currently known. If it would decay, it would involve the production of lower mass particles (such as the neutrino), but all known particles with lower rest mass have no EM charge.
https://en.wikipedia.org/wiki/Electron
Thus, during the hypothetical decay of the electron as you say, the EM charge would have to vanish, which would violate conservation laws.
https://physicsworld.com/a/electron-lifetime-is-at-least-66000-yottayears/
Thus, in the standard model, we consider the electron as a fundamental particle that, in isolation, cannot decay.
