Is it possible for the plane to become "imbalanced" and tip, especially considering the cargo was probably only people's holiday baggage?
Yes it is, very possible,
I believe on British Airways A320's u r only allowed up to 2000kgs of weight in the rear holds with nothing in the front,
thats only about 160 bags at the standard charter weight of 13kgs per piece,
I dont know what standard loading is on the MYT A320's but if most of the bags are in the back then you have a load of passengers there as well and nothing in the front it could cause problems.
F.T.L