Theoretically there is nothing that will stop a species from evolving into a previous form, but to my knowledge there are no examples of this.
In the span of a billion years a lot can happen, if the environment changes so that the species needs to adapt to it, they will evolve to meet the new environments requirements. Then if the environment changes back to a previous version, the species that live there will either move or evolve back.
Keep in mind that the chances they will do this are extremely unlikely and even if it does happen, do not expect them to look 100% like their similar looking ancestor. Imagine the differences between foxes and dogs for help on this (just an appearance comparison).
For your 700 subspecies, chances are that if the environment changes back, that many will go extinct, some will leave and some will change. 4/700 is almost .5% so it is in the realm of reasonable doubt that .5% of the subspecies will evolve back into a previous form if the environment allows it.
So the answer is yes, but with a big ol' asterisk.