While posts may be re-numbered if previous posts are deleted, that should not matter, as the link does not refer to the post number, but the system id of the item itself.
The full link is, for example:
http://www.pprune.org/ forums/showthread.php?p=2710189#post2710189 - as you can see, there is no reference to the post number - this would be generated when the thread is composed on the page.
I have to admit that the above is partly my assumption about how it works, and I stand to be corrected.
SD