I got an idea from this post to make a realistic AIM-7 Sparrow missile. The idea is, the missile uses a rocket for propulsion, and a tiny missile for guidance. This will solve the problem of in-game missiles:

Missiles guide when their rocket motor is active. If it runs out of fuel, it stops guiding. The missile's rocket motor has to burn to the target. However, in real life, for example, a Sidewinder's rocket motor burns for a few seconds and then runs it out of fuel. Then the control surfaces guide it to the target.

So, what I would need is an AIM-7 body, and put a tiny guardian in it, and a rocket for propulsion. The rocket would need a detached to remove it before it exploded. It would burn for several seconds and then then burn out.

However, the missile would just be for guidance, and the problem is, missiles produce smoke. But if the XML value IgnitionDelay=0.01 is added, the missile will not produce smoke, and it will still guide.

There is one thing that is needed to make it work: to know how long the AIM-7's motor burns. In the case of the AIM-7E-2, it is 15.5 seconds. So, the XML value burnTimer=15.5 will make the rocket burn for 15.5 seconds.

The thing needed to make this work is the knowledge of a missile's burn time. Publicly available info might not be available about the burn time of a certain missile. American ones will probably be available, Russian ones might not.

This method can be used to make other missiles.