[Battle for Whiterun bugged, Imperial side]

I have a feeling I'm going to be too late to help but I have a solution. It's not perfect but it works.

(I had the exact same issue after whiterun siege).

In the console type:

prid 6a167 (and then press enter)

Then type: disable (press enter)

Now type: prid 17055 (press enter)

Finally type: enable (press enter)

 

This should fix the drawbridge issue with general gameplay, although if you come across any scripts which open and close whiterun gate I can't vouch for whether or not they will work.

I hope I wasn't too late in helping but if anyone has the same issue this should work.