in the comments of last Friday's strip, but the summary is: Eric saved Tim from rotting away in a Chinese prison, and then disappeared in an avalanche. And Margo got to meet the Dalai Lama. It's worth looking in the LLoA3G archives for July to August 2008 to see Margo in India. The white part of India, I mean.
Anyway, the fact that the Ghost of Eric Mills is now having a conversation with his brother Tim likely means that Eric isn't a one of Margo's hallucinations, but is actually just your typical soap opera avalanche survivor. I am shocked that he didn't come back with an eyepatch and amnesia.