Mr Boney is just the game's "get out of gaol free card". Other DnD games have had the same idea of getting you back on your feet when you have cocked up; usually for money. Our saviour is clearly related to Jergal, since he spouts forth about erasing the dead character from the book of the dead when resurrecting.
It's cute that they use Jergal to link back to the BG1/2 story, but inconclusive as to whether this is the big J himself, or an important acolyte. I didn't really look closely at the Jergal statue in the crypt, but I did not get a sense that it exactly resembled Mr Boney, so they can probably make a decision on that later in development.
I would have to wonder ( at this point, anyway ) what Jergal would be doing loafing around in a minor crypt in the back of beyond, and why he would want to then loaf around in our camp. There would have to be a good rationale for such behaviour, so I would lean towards an acolyte ( who would naturally copy Jergal's characteristics ) being more reasonble, but who knows.
