Well, there are ways to extend the life of the emitted smoke particles, but I don't think they will survive the disappearance of the actual emitter itself.
Editing the length of time that each particle lives may also change the way the trail actually looks. Typically each particle disappears after a certain amount of time, while other particles are still being emitted, so you get the illusion of smoke dissipating. By increasing the lifetime of the particles you may end up with smoke falling to the ground and actually through the ground. This would increase the overall lag as well. Even when a particle falls through the ground it is still being tracked by the game engine, and still increases lag even though it is not visible.
In Gmax or 3dsmax, you can find the settings for number of particles, weight, life-span, and motion in the roll-out of the emitter itself.
