Update (Aug 2012) Aero has now essentially moved out (after the birth of our son Jasper), and is being cared for by a network of elderly neighbours. Wispa's loyalty however is unfaltering, and she passively endures consistent toddler abuse.
Update (Nov 2013) Aero is around more often now, we now see him several times a week. Not sure what has changed. Wispa is resigned to being chased around the house, mornings, evenings and weekends.
Update (Sep 2016) I am asked for updates on this topic surprisingly often, so here goes: both cats are well. Wispa now endures abuse from two children, and Aero is alive but ever fatter and never around.
Update (Sep 2017) We are about to return to the United States, and decided that Aero was better off left in the UK with his new ``owner". Wispa's loyalty is to be rewarded with her second international flight, Gatwick->Reykjavik->Chicago, at which point she will return to being an inside cat.