There are so many variables in the case of the ex.. such as, are there kids involved? How long have you invested in this relationship? etc. So
in a nutshell, I gonna tell you, hell no!
I believe that two people who have lived, loved, and MADE love to each other cannot put all that behind them and move on with their lives while still living under the same roof.
For one, y'all may still be sharing bills, meals, bathrooms, the remote, and most possibly a BED. You two may still need to make major decisions together on your everyday lives that only brings y'all closer than you really need, or want, to be. I understand that co-habitation is no longer done only to commit a relationship between two people but also to cut some costs as well. Nonetheless, there needs to be some sort of cut-off date or ending point to this arrangement if the two of you have truly decided to call it quits. There's no reason to live uncomfortably as friends or "roommates" if y'all couldn't make it as lovers. Go back home to momma if you have to or get up and get your own place. Time to make a change. Somebody's got to go.
As much as you believe you can still remain friends and move on with life, it will get real complicated when one of you starts dating again or starts bringing your own crew of friends or family over and introduces the other as "just a roommate". What if you need to bring your new boo over on a late night? Or even in the mid-afternoon. It would be pretty disrespectful doing so, not to mention really uncomfortable if y'all get caught. When one of you cooks dinner for yourself and leaves the other starving, all hell could break loose. Trust me, it may seem smooth at first, but exes have already decided the relationship can't work at any cost. Beyond countless tries to restore this union, it would be best to give yourself a span of time it will take for you to get up on your feet and out of there.
While you're still there contemplating what makes the most sense, try to set boundaries in the crib. Like whether or not y'all are gonna play like bed buddies or whether you will continue to look out for each other regarding the cooking and cleaning. Don't just up and leave somebody hanging with bills over their head either. Make sure you both have enough time to sort out the financials and handle each of your responsibilities to each other. Make an agreement as far as to what kind of guests you agree to have up in there (and when) and stick to it.
Lastly, try to make sure this relationship is truly final. If there's still any inkling of love there, explore it. Because once someone moves out, there is slim chance for a return.