The text does indeed seem to state that he cut himself off from all contact with the Universe, locking himself up in a poky little pocket universe for all eternity. I simply don't believe it. It's such an unbelievable thing for him to do that I'm not even going to bother arguing about it. He may indeed have cut himself off from the Universe for a time, but no way did he do so without having the means to reopen contact at will.Adv 12 establishes a cutoff point for Yaskodray on p32... 250,000. years after creation of the pocket universe, itself defined as "more than 300,000 years" old... (p.31).
This also means that the Aslan either were either: added by some droyne else pretending to be Yaskodray; added by yaskodray before -48,000; added by yaskodray after he thought he'd ordered the contact with the prime universe cut off; or added by the Droyne in the prime universe themselves.
-75,000 is the time the coyns first show up on those widely scattered Droyne worlds, meaning that they were first introduced then. The changes came later, 'over time'. The only thing that would prevent him from going on a walkabout around -1000 would be if he would actually cut himself off from the universe without the ability to get back in contact again. So he blew the bridge up behind him; that doesn't mean he can't rebuild it. He is an ultra-genius, you know.MT Ref's Companion sets the introductory date, too, BTW.
Recovery: On about 20 worlds, however, this did not happen.
Around -75,000, the Droyne on these worlds seem to
have almost simultaneously undergone a “renaissance.” The
key to this recovery was a revival of the ability to caste; this,
in turn, seems to have been based on the introduction of a set
of small gold disks, called coyns, which became the basis for
many aspects of Droyne culture.
(MT RefComp, p.54)
Hans