Epistemic status: Big if true/I am clearly an idiot for even posting this.
Some apparently real journalists have been approached by (& approached) several intelligence officials, some tasked specifically with investigating UFOs, who claim that the DoD has had evidence of alien intervention for a while in the form of partial & mostly-whole fragments of alien aircraft. A followup article where the publication outlines how the editors verified this persons' and others' claims and affiliations is here, and a part 2 is expected tomorrow.
For some reason - very possibly because it's complete nonsense, or because they haven't had time to independently verify - the story has only been picked up by NYMag so far. The consensus among the people I've been reviewing this article with, is that it's either a complete hoax (i.e., the entire thing nearly top to bottom is some deliberate deception) or there's a non-negligible (>5%) chance aliens are here. I would love for someone who has a good understanding of the material to give an explanation (including possibly on priors, just thinking clearly about the content of the article) of why my friend group should discount this out of hand.
Thus far I have been unconvinced by most stories of why we should to-the-point-of-not-caring-about-UFO-sightings-expect Aliens have to be big and obvious and tile the universe with fun, as opposed to operating some sort of noninterventionist monitored lightcone.
There's a lot of stuff that scares me about that post.
Resolution Criteria
Weird Explanations
Some of these seem poorly phrased, from the perspective of a lawyer.
I know you don't intend most of these interpretations, but many of them are reasonable interpretations of your literal words. I worry that you're playing with fire here and that you could end up in some nasty disagreements when it comes to resolve your proposed bet.
Overall, I feel like you're conflating "standard atheist materialists" with mainstream science and mainstream beliefs. They all differ slightly from each other. Some of the stuff on your list I'd bet my life against, but other bullet points are (when read literally) technically true.
That said, I really like your willingness to place wagers (especially in contradiction to the mainstream narrative) so that you actually have skin in the game. This is the way. I don't want to discourage you.