The idea that Nicole might have gone off someplace willingly (using her father's words) is not at all surprising or even unusual. Children do this, even street-proofed children, and they go off with total strangers as well as with people they know to some degree. Sharin' Keenan went off with Dennis Howe, who was a complete stranger. Marianne Shuett, kidnapped from Kilbride, ON in 1967, went willingly with a strange man in full sight of a number of witnesses (who presumed he was a family friend or otherwise legitimate).
(see thread here:
http://www.websleuths.com/forums/sh...bride-Ontario-27-April-1967&highlight=schuett )
I see some possible parallels to the Schuett case in Nicole's disappearance, though the crimes are not likely connected.
Woodland, I am interested in the reasoning behind your theory that Nicole may not have vanished on the day reported but at least a day earlier -- it certainly explains (if true) why no witnesses reported seeing her leave the building on the day in question, but presumably police put some credibility in the evidence of the friend and possibly others as well. However, reviewing all the evidence in the case, and entering it all in a database, may indeed lead to some potential solutions, as it did in the Schuett case, when new investigators re-opened the cold case 20-some years later.
As for the parent not reporting her missing until hours later, while most parents I know would not be so dilatory, a family friend who was a very laid-back parent allowed her children fairly free run of their (safe) neighbourhood, and when her five-year-old son was late to dinner she did not immediately think anything was wrong; she had his siblings check up and down the street and did not call police until after dark.
They found the boy drowned in the nearby creek. No foul play, an accident. Some parents let their kids have more freedom than we (or certainly I) think advisable. This was around the same time as Nicole's disappearance; I doubt many moms would be so sanguine now.
I suspect if Nicole was abducted by a stranger, she was likely killed within hours, days at most. That makes me think of the Jessop case; some evidence suggests Christine was kept by her kidnapper for at least some period of time -- IIRC one or more of the items of clothing found on her body were not ones she was wearing when she disappeared.