Is energy conserved when some of it is converted to heat?

that is what energy conservation means

energy comes in many forms and has a numerical measurable value for each form

the sum of all forms is the same

as it changes when it takes the form of heat at the lowest temperature it cannot be recoverd any other form

yes the E= mC^2 energy of atomic nucleus in the sun eventually becomes heat at the temperature of outer space around 3deg absolute. on earth it becomes "room temperature"

Yes it is.As you said energy that seems to be lost is simply converted to other types rather than destroyed.Example:You are driving your car and apply the brakes to stop.Chemical energy in the gasoline is converted into thermal energy (heat) as the engine burns it.The engine converts it into kinetic energy (movement) turning the drive train and making the car move.You apply the brakes (increasing the coefficient of friction between pads and disk) and the friction converts kinetic energy back into thermal energy (heat) which is dissipated into the atmosphere.

Yes, but heat is energy.