In the standard model the (proton, electron) is the lightest particle charged under the global (baryon number, lepton number) conservation respectively. So the

In the standard model the (proton, electron) is the lightest particle charged under the global (baryon number, lepton number) conservation respectively. So they are truly stable according to the SM. However, there are many good reasons to expect that physics beyond the standard model do not conserve B or L (or B-L, which is what's actually conserved in the SM). In those models one expects proton decays for sure. However, even in those models, electric charge is conserved. Unless there are gauge-variant dynamics at very high energy electric charge will always be conserved and electrons (and positrons), being the lightest electrically charged particles, will be absolutely stable.