Also your data isn't gone. It is still in the CSV file you imported it from. Re-import it.
Writing some VBA is a simple process if you're a programmer. I wonder how many genetic researchers fit that description?
P.S. when I said "too late to fix it", I meant by some process within Excel. Of course you can re-import the original file, but maybe you only notice the problem after you've done a lot of work with it?
Do you/have you worked in a corporate environment? You seem to have an idealistic view about how end users are expected to use Excel.
The original comment I responded to said they regularly imported large data sets and the in the case of the genetists they also are regularly importing data into Excel. In other words Excel is a regularly used and fundamental tool to their work. In this case I would expect someone to learn the basics of using it. Just as I would expect a developer to learn their editor, build system, version control system, etc.
The fact is the person was double-clicking a file in a list to view its contents and Excel was trampling it. Nobody in their right mind will waste time to open Excel first, use import feature, re-navigate to the file they were already looking at, and go through the import dialog just to see what's inside.