what the suburbs notably lack is any transportation infastructure other than private autos.  so in a fuel-poor future they might easily split off into townships quite separate from the urban cores they sprawled out from.  the yuppies with no survival skills who built and originally inhabited them might leave, but I think they would quickly become microfarming belts, with each ridiculously huge house as you say, occupied by more than one family or by extended families.

the real problem is the quality of construction, for whuch in many cases "gimcrack" would be too kind. w/o endless inputs of repair/maintenance I don't see the average carburb home standing up well over a 40 year period.  the structures are so flimsy that they rely on high-tech and lightweight roofing materials -- anything heavier wouldn't be borne by the spindly little wall joists.  I imagine that creative survivalist families and townships would encase the entire structure in strawbale and adobe (or cob or whatever was locally available) to improve insulation and create a stronger perimeter to support more traditional roofing materials...  but this is idle speculation and more appropriate for a sci fi story than our immediate discussion...

The difference between theory and practise in practise ...