I am not a lawyer but I would find it hard to believe that an authorized person from the association could not get authorization to go into the unit to secure it or winterize it. I think if it is truly the lawyer that states that no one should go in, then the lawyer can easily file a motion to gain access to winterize the unit. I don't see any court denying a motion to secure a property.
Whomever you spoke with at the management company is misinformed in my opinion.
But lets assume the worst. I have been a witness to this very scenario. An upstairs abandoned condo had its pipes burst and the water ran for aout 36 hours into two lower units. Obviously the condo was abandoned and the associations insurance had to pay for the damages to both units.
Most associations have insurance for things of that nature. But the associations insurance may NOT cover the contents of the unit. The insurance may only cover restoring the structure and coverings of the building but may not cover the belongings of the unit's owner. I would get a copy of the associations insurance policy and then call up the insurance agency and ask these questions to be safe.
I hope this helps.