I think if Musk had to wager he'd bet that this launch is not completely successful. It still makes sense to fly it though. You hope to learn enough to make the second or third attempt a success.
This isn’t necessarily true. They know that there are unknown unknowns at play here, as nothing quite like FH has ever flown. There is a non-negligible chance of something unforeseen rearing its ugly head, and if you’re just launching a lulz payload, that’s fine.
The Roadster is the PR payload. The real payload is the set of all the sensors & transmitters in the rocket. They'll be getting a lot of engineering data whether it is a successful launch or not.
I think if Musk had to wager he'd bet that this launch is not completely successful. It still makes sense to fly it though. You hope to learn enough to make the second or third attempt a success.