I was quite confident that it was Sundara being mated as I mentioned above, it was the cow that @Willem123 saw separated from Aung Bo that was up in the air. I did suggest originally it was probably Maya, but also accepted anything could have happened in the last 2 weeks since my visit.
When I talked to a keeper on my last morning at Chester, I was told that Sundara will be having one more calf with Aung Bo before he will leave- it was mentioned that in a few months they will find out if the matings that happened around the time of my visit were successful, and as soon as they find out Sundara is pregnant, they will start organising the departure of Aung Bo, although a future successor hasn't been considered yet.
If Sundara is in fact pregnant, it would make sense to move Aung Bo elsewhere now to allow there to be the space one the new baby is born (and to also accommodate Anjan as he grows before he too will be transferred out).
Considering Anjan's not even five yet, I don't think he would be the one being transferred just yet. It would also be beneficial for him to still be around for Sundara's next calf as well.
I would anticipate they’d wait until not only is Sundara pregnant, but several months into the pregnancy before they transfer Aung Bo out. They want to ensure she will carry the pregnancy to term and there’s no harm in waiting a few more months.
Considering people on here were speculating Sundara was pregnant a year ago (and it’s been in the plans), it’s possible she may have already had an early miscarriage (or failed to conceive on an earlier cycle) if she’s only recently been mated again.
With regards to Aung Bo, we haven’t heard an announcement from Chester that the EEHV vaccine trial (which he’s participating in) has wrapped up. For the sake of consistent data, they can’t disrupt this trial by moving him to a new location, so this may also influence the timing of his departure.