If you're really crazy and have a few hours, you can look people and free companies up on the community site, and inspect their class levels and the gear they logged out in.

I used this for one housing area (all 8 wards) to determine a "high" or "low" probability of abandonment, by this criteria:

Players:
- Does not have a character above 50 (didnt buy HW)
- Has 1 lvl 60 and is still in HQ 'quest' gear (likely did not log in since 3.1)

Free Companies:
- Has less than 10 members
- Has no weekly AND no monthly standings
- Players meed the criteria above

This is by no way a guaranteed system, but about a best guess as I could come up with. By the number of "high" probability houses expiring, the housing area I looked up was set to relinquish about 18% of it's current residents.

(yes, I did this, and I am in fact crazy. *nodnod*)