Is it possible for a city to un-annex land?
One of Detroit's problems is that there are huge tracts of land that are sparsely populated that it's technically responsible for as they were annexed and developed as part of the city in the past. Given the problems, if they could divest themselves of that jurisdiction and let it become county land, it would free them from the costs to administer it. Obviously there'd need to be a plan formed to transition those living there to other services, but around where I live, county lands are served by Rural Metro Fire Department, a private fire department that one pays a subscription to (or else gets billed for the cost of fighting the fire) and the county sheriff provides policing. Most utilities heree aren't city-provided anyway, though they'd have to figure out how water, sewer, and trash would work, but without the city collecting taxes in those areas, the residents that choose to stay would have a little less taxation and could probably figure out how to afford to make it work.
For this to work, there'd need to be some kind of guarantees on the parcels that the city couldn't re-annex them immediately if things turn around at the landowners' expense...