I can offer some insight -- as I list bank owned homes for Fannie Mae and other banks.
The answer is -- it depends.
If it is a Fannie Mae or Fannie Mae backed home, the bank will almost always pay for the de-winterization and then winterizing it again. After that, you're on your own to do it yourself after ownership.
Freddie Mac will make you pay for the cost of doing so, with the exception being in cities with a C of O requirement, you may be able to time your inspection for purchase during the period that it is on to save some money.
Most banks will charge you a fee to do it and use one of their contractors for liability purposes. You can try to make it part of your offer, so see if your agent has any luck getting the asset manager at the bank to ok such fees. Chances are if you made a good, solid offer you'll have better luck with them being cooperative for this and other repairs that may be necessary.