git rebase is like fish.

Hours after the kill: hmm, tasty.
A day after the kill: not too bad.
A few days: time to toss this in the trash
More than a week: dig a hole and bury this thing before it stinks up the neighborhood.

That being said, I'd rather eat a plate of Hákarl than deal with rebasing a diverance that is over a month old. I simply don't use rebase. It's just too stinky. I just merge very often and keep things in sync.

If you need the effect of a rebase without the crazy hassle:
git checkout master
git checkout -b rebase_branch
git merge --squash dev_branch