It is not possible to do that with soft-links, because in the case of soft links targets are not aware of the existence of the links to them.
However, if your destination and source files are on the same partition, you could use hard links instead. With hard links there is a counter in the inode they point to, which keeps track of how many hard links (files) are linking to the inode.
You can see that counter by using the
stat command (or system call). The output looks like this, look at the
links field, it shows how many links/files are pointing to this file's inode:
~ $ touch testfile1
~ $ ln testfile1 testfile2
~ $ stat testfile1
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 803h/2051d Inode: 7062809 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 1000/ mst) Gid: ( 100/ users)
Access: 2014-01-04 10:19:27.899679948 +0300
Modify: 2014-01-04 10:19:27.899679948 +0300
Change: 2014-01-04 10:19:33.149679891 +0300
So before deleting a file you could check the stat's of it, if the
Links field is above
1 there has to be another hard link to it. Unfortunately, to find the second hard link based on an inode will be an expensive search operation, so I hope you have some kind of naming scheme to find them faster.