The question is, though, will there actually be a "fair" war between the Lightside and the Shadow?

The DO will certainly stronger mess with nature, weather and reality yet. This could lead to earthquakes, eruptions of volcanoes or an entire army simply swallowed by the earth.

Then a big problem for the Light will be food and diseases. While Shadowspawn can eat humans or carrion, the armies of the Light will simply starve and become ill. It's clear that the DO will eventually darken the sun, too, so that also hope vanishes. Maybe in the end he will even have the power to block channelers from accessing the OP (like SH can already do in small measures). Thus Mat or anyone else probably won't have a deadly army against all various kinds of Shadowspawn, but a rather poor cluster of survivors of the DO's touch.

For these reasons I think TG will be very chaotic with various desperate battles, not an actual military campaign of the Light against the Shadow. In one of Rand's futures during the Portal Stone trip we saw that the Shadow normally won't have any problem to wipe out the armies of mankind. We also know that Mat will have to blow the Horn of Valere "in the last lorn fight".

Rand has to win TG in the Pit of Doom, otherwise even the best generals of all times won't have a chance against the Shadow.