Dear Arpit,
Welcome to the forum and I'm very sorry to hear the news in your environment.
I'm afraid that there will not be any backup location such as Recycle Bin for the list column like the list items in the SharePoint Online UI. If the list column is deleted, it will be permanently deleted and can't be restored.
I suggest you first go to List Settings>Columns to check whether the list items are actually deleted in your environment and they may be hidden from the view in some scenarios.
If you make sure that they are actually deleted, please don't worry. We have a specific channel trying to help customers on recovering the SharePoint Online data. I suggest you contact the administrators in your organization if you aren't the administrator and let him open a support ticket to our related team as soon as possible so that they can see if the deleted columns can be restored by them in your environment by another way. Sorry for that our category may have limited resources on doing that.
Another way to back up the column may be to use the site column. Unless the site column is deleted in Site Column, you can reapply it to the list if the list column is deleted from the list.
Thanks for your understanding and have a nice day!
Cliff