So there are a bunch of stories where the war doesn't finish at Hogwarts and Harry & Co. go back in time to fix things. Some are good, most like all fanfiction are poor but I think the war not ending with single spell is an interesting idea. Are there any good stories about the war continuing after Voldemort's defeat?

 

Most of the time travel stories doesn't really deal with Voldemort dieing at Hogwarts but instead deals with him living and the world going to shit.

Even stories dealing with Voldemort living are rare and I only really remember one story.
Betrayal

 

Well the time travel was only a way to frame the request, I'd just like to see Harry becoming the badass veteran, fighting in the ruins of the wizarding world. There are so many stories, A Necessary Gift or I'm Still Here spring to mind, where the backstory is the long war, I was hoping for a story like that, no time travel needed.

 

The Resistance of Azkaban

The best badass veteran Harry story to date, IMO. Novel length and completed. This isn't exactly what you asked for. The war does drag on, but the point of divergence is after the 5th book.

 

And its sequel:

The first one deals with Harry's schoolyears up to the Goblet of Fire, and the second with the consequences of Voldemort's fall. I followed the first one as a nice timewaster though I never read the sequel (yet).