I've heard of things disappearing. I won't do it based on the horror stories reported here.
Plus i have several things that right now are in violation of the current placement rules. Like the cars on streets that were once allowed but now aren't. Many things on dirt that were allowed but now aren't.
My town is becoming a wreck though and I'd like to restart, but I'm just trying not to do anything drastic. I never could rebuild KL and i suspect nuking would just end my participation completely.
So think it through. Maybe start in one corner you make completely empty, rebuild that, than work the next section, etc. Take human bites.