A combination Debris hut / Tarp shelter where the tarp is primarily the roof over an increasingly reinforced Debris hut type shelter may last and suffice for a 3 month duration. I don't think that it will be adequate or comfortable but it could suffice for the time it takes to transition to either "back-to-normal" / recovery mode or to the long-term scenario where you are building a cabin to replace your tarp. The longest you could get something like to work would be 3 months but I believe that you are right in thinking that you would want to be in some other type of shelter before then. I am considering the 3 week - 3 month scenario something like "lost at sea, stranded way off course in the outback, or perhaps aftermath of very b ad hurricaine (hurricaine andrew was bad enough that some didn't return to their homes or newly built homes for more than a month but all were back fully into recovery - go back to work mode after three.