In the description of polymorph, it states that
The target’s game statistics, including mental ability scores, are replaced by the statistics of the chosen beast.
And this sage advice clarifies the meaning of “game statistics”, which are meant to also include class features.
So it seems reasonable to interpret this as to say that an abjuration wizard does not have Arcane Ward up while under the effect of a polymorph spell, since it is a class feature. But when the wizard reverses to their original form, does the Arcane Ward come back up?
By the description in the PHB, p.115, there is a relevant remark:
Once you create the ward, you can’t create it again until you finish a long rest.
which suggests that it can end by some method. So when the effect of polymorph ends, does the wizard no longer have Arcane Ward up, therefore having to wait until the next long rest to be able to raise it again, or does it return in the same situation as immediately before polymorph entered into effect?