http://en.wikipedia.org/wiki/Laki#Conseq..._in_Europe
Just reading up some more.
According to Wiki:
"The weather became very hot, causing severe thunderstorms with large hailstones that were reported to have killed cattle,[17] until the haze dissipated in the autumn. The winter of 1783/1784 was very severe;[18] The naturalist Gilbert White in Selborne, Hampshire, reported 28 days of continuous frost. The extreme winter is estimated to have caused 8,000 additional deaths in the UK. During the spring thaw, Germany and Central Europe reported severe flood damage.[9]"
The poisonous gas cloud mainly effected outdoors workers, so it should be pretty manageable if you're able to be inside for much of the time.
The number of variables is pretty high. But as long as you have enough food and water to last the time the gas is around, and you stay indoors a lot, you should be okay. The real problem will be if an event like this happens when already in a post SHTF situation, and we get no warning about it from the news or any government agencies!