No, it's a nice (conspiracy) theory, but it would be just too much. Three reasons which speak against this theory are:

• As mentioned above 2008 was his "worst year", I don't think that he had time to work on a project like Bitcoin, especially since he was busys with SpaceX and Tesla.
• Elon Musk is someone who seek attention and appreciation, I guess that inventing something huge and then quietly disappearing, just wouldn't suit his personality (and ego).
• After PayPal, I'm not sure if he wanted to do something with electronic cash again, especially something that has a fundamental different approach.

According to "Banking on Bitcoin" (a documentary I'd highly recommend) Satoshi was actually Hal Finney or Nick Szabo or both.