Spoilers Off apply to all moment pages, so proceed with caution. You Have Been Warned.
Empress Tihana would have poisoned everyone with the fountain water and turn them into harvesters either way. From the moment Tihana crashed the plane, their fates were sealed.
Considering the ethereal calmness and darkness that Daniel comes to after getting taken by the Shadow, the fact that Weyer and Agrippa seem to be calm, well off, and in control, they're all probably in a different place than Alexander's home world. It almost seems like Weyer and Agrippa have ascended in some way, Weyer managing to gain control over whatever dimension hopping he's been doing. It seems unlikely that Agrippa's head just popped out into the ruined city and then made sympathetic pleas in the afterlife for Daniel, considering how Herbert ended up.
Assuming they weren't just killed by the tower collapsing, they'll end up taken/eaten and sent to the same darkness Daniel ended up in, and could end up being "helped" by Weyer and company.