Is this fixable? If so how or wat would u do? Or just replace?

 

Wow. That's some pretty bad damage. Might be best to cut it out and weld in a new one.

 

It's a tough spot to fix. If you get under there and remove the plastic shield protecting the filler areA, you will see that there are a few panels joining there. Even if you replace the quarter skin, you prob have nothing to attach it too. The whole area often rots out from water collecting in the trunk. The quarter skin is actually very difficult to replace, so you would probably be better off patching it and the area behind it. Might have to replace the frame rail too.
I know I say this all the time, but if the rust is this bad in that location , it's just as bad or worse in some other key areas. I believe you posted that you have floorboard rust as well. I think you will want to seriously reconsider if that body is worth putting any work into it. I'll post some pics of the area under the filler for you so you can see what under there.

 

At this point I would get an angle grinder out and cut the hole out until the rust is gone. Then I would buy a new rear fender skin and use just what I need after fixing the inside. I had a similar issue last year
https://www.thirdgen.org/forums/body...one-wrong.html

 

Trust me this car isn't going any we're any time soon no matter what and I think I'll do the repair u did that can out really good