Yes, guters were just installed. However, there weren't gutters before 2 weeks ago. So, for the past 12 years, no gutters COULD have been the problem.
And yes, it's possible that there is no longer a direct water problem. However, the rotted wood problem still exists which is the core subject of the post. It's not enough to just put in gutters. With negative slope or simply over-flowing gutters (improperly installed ones) will exacerbate the problem. A broader view must be taken which includes evaluating the gutters and the install. If they empty next to the foundation with negative slope, he might as well not have gutters. The downspout should be extended at least 3' from the foundation with positive slope. And, this may STILL not be enough to solve the problem.
Now, what to do about the rotted wood??? Have the home inspected for 'broader damage', then have the inspector give you an estimate as to what it, among other things, will cost to have fixed. If he's ASHI-approved, he WON'T offer to do the work. If he does, report him to the WEB site I cited.