What happen if ammonium chloride is heated?

It actually decomposes in ammonia and hydrogen chloride. It’s possible to separate them, because ammonia is lighter, so if you heat it in an inclined tube, the ammonia will go up and the HCl will go down. You can detect both gases with wet indicator papers put up and down the tube. Of course, when the gases cool together (if you don’t separate them), they recombine to form NH4Cl, and it appears that it sublimated.

The two will react (ammonium chloride is mildly acidic) to produce ammonia gas, calcium chloride & water vapour.

Ammonium chloride is salt of ammonia and hydrochloric acid, both are liquid at room temperature. It is very much volatite at room temperature. Ammonia gas releases with hydrochloric acid. Ammonia have boiling point - 33°C, means it is very much volatite. That's why it is u stable at room temperature.

It sublimes as the solid NH4Cl turns into NH3 and HCl, both are gases, i.e. a reverse acid-base reaction.

On cooling, the two gases react (proton transfer) to reform ionic NH4Cl.

It all depends on the situation. If you have Ag(1+) ions in the solution and you add NH4(1+)Cl(1-) to it, you will get a precipitate of AgCl. That won't happen with the nitrate salt.

Ammonium chloride undergoes thermal dissociation on heating. It would liberate pungent smelling ammonia gas and hydrogen chloride gas on heating.

NH4Cl ➡➡NH3(g) + HCl(g)

On heating strongly above 340 degree C, the white solid ammonium chloride, thermally decomposes into a mixture of two colourless gases ammonia and hydrogen chloride.
On cooling the reaction is reversed and solid ammonium chloride reforms.
This is an example of sublimation but here it involves both physical and chemical changes.
When a substance sublimes it changes directly from a solid into a gas without melting and on cooling reforms the solid without condensing to form a liquid.
But, more importantly in this section, it is an example of a reversible reaction.
Ammonium chloride + heat ammonia + hydrogen chloride
NH4Cl(s) NH3(g) + HCl(g)

so the thermal decomposition of ammonium chloride into ammonia and hydrogen chloride is the forward reaction, and the formation of ammonium chloride from ammonia and hydrogen chloride is the backward reaction

I am assuming you are asking about heating solid crystals of ammonium chloride, and it depends on how strongly it is heated. In general, nothing will happen unless it is heated strongly enough to cause it to decompose. Off hand, I am not sure hot hot that will have to be, but eventually at some temperature it will decompose into ammonia and hydrogen chloride.

Both gases are irritating to smell and could be harmful if inhaled.

Upon decomposition, the ammonia and hydrogen chloride will rise as gases but then recombine to form very fine ammonium chloride particles that look like smoke.

The classical way for the military to make a smoke screen is to simultaneously release ammonia gas and hydrogen chloride gas.

If you are asking about heating a solution of ammonium chloride, the ammonium chloride (a salt) will be in equilibrium with ammonia and hydrogen chloride in the form of hydrochloric acid. The net result of heating such a solution will be to drive the equilibrium toward the ammonia and hydrogen chloride. These will be released from the solution as gases, and once in the air will combine to make the fine “smoke” consisting of ammonium chloride particles.