Personal recommendations / procedures to disable external domain / DNS entries and exchange them?

I've set up and set up more domains and servers than I can count on over the years, but it's not often that I've dealt with dismantling. In general, I would simply put a landing page for the domain with information about the reason for its removal or otherwise, but I hoped to get information on what others usually do? Are there any DNS records that you like to keep or things of that nature? The company has been bought out and so I will know if they only want the www registrations to be directed to the new property site, but anything that any one would like to recommend would be appreciated.

The Exchange server will no longer be used, everyone has migrated and is using a different system, all mailboxes have been archived with Symantec Enterprise Vault. So we are ready to remove Exchange, but we are also wondering if there are any other steps. precautions that could be recommended too?

If there is nothing special to recommend, I will end up proceeding as usual, but any personal experience and suggestions are welcome!

thank you,