Ahh. I now see the catch-22. To get you a MVD-SCL replacement for the Pluna bankrupt segment, they have to re-ticket! True enough.
The real culprit and cause of the base problem here is Pluna. An airline going belly up is not that common, so I can understand Expedia/ Lan etc. struggling with it. For the first tix, it was a surprise, and you were already travelling, and rules are in place to not strand pax and eventually Expedia/Lan did resolve it. This time you have a future tix knowing Pluna is gone. I struggle to understand why competitor airlines have to cough up and cover off Pluna tix. Here, we have a travel agents fund that kicks in when a airline collapses, this fund gets people home etc. I wonder if there is something similar there. Either way, I put the ball in Expedia's court. Why do you have to pay more, why does Expedia not cover it off with some fund for this contingency?
But to be useful, you said “My temporary solution buy a $340 MVD-SCL one way ticket on LAN, and contest $340 of the original ticket purchased from Expedia. We'll see how that works. I would not want to see Expedia lose money due to LAN's poor customer service, but Expedia is the company that took my money in exchange for an airplane ticket that will not work.” Not sure why you are concerned about Expedia, nor why LAN re-ticketing is considered bad service, but I would wonder that by flying a separate tix MVD-SCL what will happen to your original SCL-JFK segment?