Yeah, I don't think there should be much debate about who the better goaltender is. Kari is better. Kari has a pretty bad history of injuries though, so what do you do?
If you like Pavs, perhaps it's time to cut ties with Kari and get something while you can. I don't think anyone can know if he gets healthy or not with this 2nd surgery, but if he does I think he goes on to have a great career. That makes trading him scary, but probably no less of a necessity in DW's eyes.
One piece of common hockey wisdom is that you need to pick a starter, and I think it is just myth goalies have sold to coaches to get an edge over one another. I can't think of a single example where having two competing goalies hurt a team.
Goalies are fiercely competitive for playing time. For example, I read a funny story from a guy who played goal in juniors with Nurminen, Pasi used to basically just chant to him "I am better than you, I am better than you..." And it worked.
That internal competition is what hones good goalies. Part of the problem with Lehtonen may have been that he wasn't pushed to earn the starting spot, we'll see how responds to having to battle for playing time. BTW, not enough competition due to lack of depth has been an issue for this granchise since the start, ice time needs to be earned. I don't think trading away goalies so they don't have to compete is a good idea, have Moose, Pavs and Lehtonen fight for it and see who emerges.