The world exploding would not invalidate a transfer, and has nothing to do with RAP. A key portion is who is alive at the time of the original conveyance. The land does not have to vest while the original people are alive.
An easy way to analyze the situation is to take everyone alive on the day of the transfer, and have them adopt a kid the day after. The next day, kill everyone off that was present and had an interest in the original transfer. Now, do the remaining interests HAVE to vest in 21 years? If so, then there is no RAP violation. If not, then there IS a RAP violation.
Furthermore, a violation only invalidates the specific part of the transfer that is a violation. It does not invalidate the entire transaction.