Django's upgrade/deprecation policies are pretty well documented, but if a project is going to be unmaintained for a long time, and you're trying to, say, upgrade a Django 1.6 app to 1.9, you're going to be in for some pain, as in three versions a feature will go from supported, to quiet-deprecation to noisy-deprecation to absent. If a project is not going to be maintained to track the "latest" Django, it should target one of the LTS releases - 1.8 currently - which will have support till 2018.
That will give you security and data-loss-bug updates, but won't give you new features. If you wan't those, then you need to track the current version. If you really are stepping through 3 or more versions (or fewer, if it was already using a deprecated feature) then the best bet is to go through the deprecation documents and convert things over... or just re-write. Sometimes that IS simpler. And, of course, target a LTS if that's appropriate.