@Master Zik
to answer your question, we're not sure but signs point to yes.
there were 2 people present when Robb was signing his Will (what it turned out to be)
Rickon and Bran were thought to be dead, Arya lost/dead, Sansa a Lannister,
which only left Jon
but there were 3 factors. (book wise)
1. with the north sort of in fractions, Robb technically didn't have the power to that
2. Sansa was still alive
3. Rickon is still safe and sound with the umbers
4. Jon refused to be legitimatized by Stannis
(show wise it doesn't work because)
1. Sansa is alive and not only a stark but a bolton, Boltons are recognized by the crown to be wardens of the north, she is both and possily pregnant (which is why ramsay said, i will always be apart of you")
2. glovers shut them out. and that was suppose to be one that knew about the legitimatizing if there was one.... mormont too.
Manderly's still haven't been heard from in the show either.