1. Try the column and see if it still performs as it should. It might be OK after all this.
2. Even though HPLC columns are expensive, you and your supervisor need to realize that these are CONSUMABLE ITEMS, just like vials, filters, etc. When one calculates the cost of the column per sample or injection, it's typically not that high, just looks like a "big hit" when it gets ordered compared to a package of autosampler vials or similar. I always had a brand-new spare column in-house to throw in for either troubleshooting or to have on hand if a column no longer performed. Maybe part of your job will be to educate the supervisor that these are consumable items. I'm also betting that you never forget ever to cap a column !
3. That said: several times I came across a column left uncapped in our lab, and can't respond that these were all or dead, or even a majority of them. This happened a lot in the 1980s-1990s when we used modular reverse phase columns from a company named Brownlee, later bought out by Perkin-Elmer; these columns did not have a screw-in end fitting, they fit in a holder, so the 1/4 inch o.d. tubes were simply "capped" by a little vinyl cap. So these frequently were left open to the air by neglect.