The chemical decomposes rapidly and will, in its post-burn quantities, will remove itself within 2 weeks. Wildlife will die off during this time but it's not a permanent poisoning.
Hmmm... [citation needed]
Have the EPA.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://semspub.epa.gov/work/05/437069.pdf&ved=2ahUKEwj90IuthKD9AhVmJkQIHeI-D0IQFnoECB8QAQ&usg=AOvVaw1mEWCjk6kPzM3YUTRIAE2hIt is very volatile in water, evaporates with a half-life of up to 0.5 days. Once in air it decomposes with a half-life of about 1.5 days.
All the justifiable concerns about poor regulations seems to have precipitated some fearmongering about this particular incident. I've heard people saying vinyl chloride is one of the most dangerous chemicals known to man (not even close). Same with the armchair detectives saying how the balloon reporting is about distracting from this when literally everyone is talking about this and it's everywhere.
I will say I'm not an environmental scientist. Also I'm not sure how the fact it was burnt changes the calculus, burning chlorinated stuff can make nasty stuff sometimes. It is true burning vinyl chloride is likely to make acidic HCl gas accounting for the feelings of burning in eyes & mucous membranes that have been reported but that is not a persistent pollutant. The most concerning thing that can result from the burning seems to be phosgene gas. It is unclear how much was made but it is very plausible that it is not significant as environmental air monitors have been reported to placate concerns.
EDIT: Did some more digging. Phosgene is a minor combustion product of vinyl chloride:
https://www.tandfonline.com/doi/abs/10.1080/0002889718506429 . Phosgene and carbon monoxide products are acutely highly toxic but are also gaseous, dispersing in the atmosphere.