This is mostly just my opinion, but in the past,
ABD has normally not "required" stuff like that. If you can't enter the country, it's your problem. If you don't have a valid passport, not their problem, it's yours. China requires a Visa to enter mainland China, and if you don't or can't get a Visa, and can't enter the country, you are out of luck. ABD will tell you this up front. So they may say that being vaccinated is required to enter the country, but that doesn't mean they'll require it to take the trip. So if you're not vaccinated, it's your problem. Now, of course, a lot of stuff is still not normal, so anything is possible. But I really see them putting the onus on the customer, and not on them (because you could argue you need a refund because they won't let you take the trip, and they might argue you had to cancel because you wouldn't or couldn't get vaccinated.)
Is it an Adults Only trip? Because if it's not, it will likely still be cancelled if kids can't be vaccinated by then.
Sayhello