When electrons flow through a conductor it is subject to resistive loss, which has the unfortunate capability of producing heat from this current, leaving us with less current in the other end of the conductor opposite to the power source.
When current is lost due to heat, what happens to the electron? I mean, what is left of it? I guess heat is caused by friction, but that doesn't mean that the electron is not able to travel all the way through to the load of the conductor, or what?
The electrons don't "go" anywhere, and current (the net flow of electrons) is not "lost" to heat. But the electrons gain energy through the application of an electric field, and they can lose that energy through inelastic interactions with the other particles (nuclei) in the conductor. The energy lost is in the form of randomized vibratory motion, which is just another way of saying "heat".
If you want a more detailed answer, you should ask on the Physics SE.
No, current is not lost due to heat. The same current flows in one end of a wire that flows out the other end, regardless of how much heat is dissipated in the wire (or any other resistor).
Energy is conserved because the resistance times the current causes a voltage drop. This voltage times current is power, which is taken from the circuit and heats the resistor. The voltage drop in the resistor means there is less voltage available to the rest of the circuit, but the current thru the whole loop is the same.
This is similar to a turbine being driven by high pressure water. The same amount of water comes out of the turbine as goes in, but there is a pressure difference between the input flow and the output flow. It is that pressure difference (analgous to voltage) times the water flow (analogous to current) that represents work done, which goes to spinning the turbine.
In modern understanding and most simplified terms, resistance of a conductor is caused by colliding of electrons with collective oscillations of atom lattice of metals, called "phonons". Oscillations of lattice can be considered as a "gas of phonons", which actually determines/defines the temperature of a conductor, and all classic thermodynamics therefore apply. In process of collisions the drifting electrons lose their energy, so an external electric field is needed to maintain their flow. See more explanations in this nice Wikipedia article, "Electrical resistivity and conductivity".
Electrons are particles with very special nature. They behave as a matter with mass and speed and when collide with other particles they produce heat. Another nature of electrons is the magnetic field that accompanies the electrons when they change their direction. This unique nature that is not found in any other particles rather than electrons do the real magic.
So electrons don't vanish after being used but rather they return back to their original sender after doing the required work. They are like labors with special skills when their manager sends them for a special task by giving them some incentives and they return back again to the same manager after they finish their assigned task when he can send them back to another task with the appropriate incentives.
For example if we need a motor to rotate, the power supply (The manager) asks the motor (the client) about how much labor it needs to rotate for a second. The motor calculates this through measuring how much rotating force it needs to overcome the mechanical resistance of the rotating parts and then rotate them with the needed speed.
Knowing that moving electrons in a magnetic field yields a rotating force what now is needed is sending the correct amount of electrons (labors) for this second that are capable of producing the needed rotating force when they cut the internal magnetic field of the motor. This amount of electrons in one second is the current intensity and to continue for more seconds the power supply (the manager) should have the power to send the same amount every second so it should have the needed incentives to force (persuade) the required amount of electrons to go to the client and do the required job.
The incentives can be also another magnetic field but this time applied at the electrons in the power supply (the manager puts their labor in a very tense situation that forces them to go forward) this magnetic field is applied on the electrons while they are rotating using another form of energy like water falls or pressured water-vapour.
To continue sending the electrons (the labors) the manager must continue paying the incentives (Boiling water for example to produce water vapour). That is why we need to consume some type of energy to produce electrical energy.
Every atom has photons captured into its electronic orbits. The total number of photons determine the atoms temperature. If it happens to be an atom in an electric circuit, if the electrons are induced to move, the photons move along with them although at light speed. The photons do the work of heating and lighting in the circuit. Electrons are not capable of doing this. The photons move from atom to atom but when they are moving it is at light speed. This is how telephone and telegraph signals move at light speed. Photons can do work because they carry energy. A photon can not exists without energy. I don't know if energy can exist without the photon. It may be the two words are synonymous.
