Bug ... (that might come out from original version of vB)
If you has a "soft deleted thread" containing some "soft deleted posts"
If you "Hard delete" the thread, the co-responding "soft deleted posts" will be undefined ($post['postid'] will not exists, only $post['primaryid'] exists)
Check that out, and it might be a bug in vB.com too. I dont know if it is, or if it has beed reported over there.
Additional suggestion.
01: This migh not be functionally important, but has "management" cleaner.
Giving the option to manage the thread and post seperately.
Says if you have
/forum/admincp/softdeladmin.php?type=thread, it will only process the deleted threads
/forum/admincp/softdeladmin.php?type=post, it will only process the deleted posts
if no value given, do both (like what you already have)
02: CHECK ALL option. Can you make it to check all thread and check all post seperately?
03. Thread Name/Moderator Name/Thread Link phrase should be changed

I dont think you need that phrase at all.