So we don't know for sure if Lara still gets burned by his touch. It could be that the protection is gone because Karrin died. And she did die. Valhalla is the afterlife.
That is true, the protection has not been tested after Karrin's death yet. I imagine that is going to be one of the first things that we learn about in Twelve Months.
However, there might some reason to believe that her being dead doesn't really matter. It didn't matter what Susan was doing after she and Harry got separated, it didn't matter what Thomas was doing either for Justine to keep the protection, it only ever mattered what Harry and Justine did themselves to get the protection removed from themselves (sleeping with Luccio and other women, respectively).
I don't think it's 100% clear how the protection works really. I mean, in one book Thomas says Lara has a burn mark from a wedding ring, in Peace Talks it seems like it was only a mild burn what she got from Harry, but also true love is about supposed to be super rare, but Harry gets it twice in his short life (imo, it was ridiculous that he got it from Susan, but ymmv), then you have to add up some of the stuff that's been said in Something Borrowed about true love as well. It's all a bit inconsistent imo. Personally, I wonder how much of all of that is about conscious decisions. But anyway, ymmv about the philosophical concepts of what is love and all of that. I imagine that the next book will bring some clarification over this part of the lore.
One thing that JB has said though, that so far seems consistent through the books, is that the true love protection thing only happens between consenting adults, who mutually love each other and have shared the physicality of it, it doesn't take hold if you don't act on it.
IMO, it seems like a "mark" that is placed on you, that would stay until it gets removed by an act of rejection of it, ie sleeping with another person (because apparently not even time erases it, if we believe White Night).
But yeah, we don't know how death of one of the people involved affects it, my guess though, would be that it doesn't. Harry is still alive, he was already "marked" by true love, he would stay that way until he "rejects it" by being sexual with someone else.