Mixing various spoke widths in a single wheel So the story began some 4 years ago, when I bent my rear derailleur hanger while crashing, and my  chain got stuck between the cassette and the wheel scratching a few spokes. Everything was fine until this year when some of these spokes started to snap and I had to replace them. 

I have 32 DT Revolution spokes that are 1.8-1.5-1.8mm in diameter and replaced 4 of them from the drive side to plain 2.0mm spokes. I trued the wheel with no problems and after some 500km everything looks fine.

The question is: for how long? Will the thicker spokes exert more side force and lead to over-tensing the other side? Or is there a risk in quicker fatigue of spokes on either side?
Given the age of the wheel, you're going to continue to snap older spokes from time to time. Don't worry about the gauge of the replacement spoke. Assuming it's within the range of appropriate tension, as long as it pulls true there's not much to be concerned about. I have multiple wheels with some of the thinnest gauge spokes available (Sapim CX Rays) with straight gauge replacement spokes. No issues to report.