At the end of Return of the Jedi we're shown that Anakin, Yoda, and Obi-Wan are Force ghosts.
At that time they were one with the Force, their living energy had been returned to it, but they were able to maintain their consciousness and appear to Luke.
My question is: over time, did they eventually "die" properly, dissipating and returning fully to the Force?
I'm looking for references from canon or the EU, legends, etc.
NB: it's been hinted that Obi-wans ghost may appear in Episode 8, but as yet this is not official.