I think it's highly unusual to have www.adomain.tld and adomain.tld to be two different sites. Why would you want to do this? I ask because I suspect that we're miscommunicating about what "hosting the domain" means.
You're not deleting the domain from your managed domains. You're deleting the web hosting for that domain. It will still appear in the table of managed domains in "Domains>Manage Domains". You will be able to click on the "DNS" link in that table to modify the DNS entries for that domain.
It's easy to get confused between deleting the hosting for a domain and deleting the domain. You should note that there are two delete buttons for each domain in "Domains>Manage Domains". The one under the "Web Hosting" column deletes the web hosting - the apache config and the DNS entries. The one under "Actions" column completely deletes the domain from DreamHost management.
Free unique IP and $67 off with code [color=#CC0000]LMIP67[/color] or use [color=#CC0000]LM97[/color] for $97 off. Click for other Dreamhost coupons / promo codes