That sounds nasty...
Have you managed to jack the car and take a look under? Take some photos of the suspension struts, front arms and where they join the car - might help us identify the issue. Might be a recovery to garage job....i would have thought it be a pretty significant failure for the suspension to drop like that.
There is a corrosion issue on the steel front arms used on the newage wagons which can lead to failure, but normally one side will go, strange for both sides to drop evenly. Has the car ever had the arms checked by a Subaru dealer? They issued a recall a few years ago to check all steel arms - they tested them by firing a spring loaded spike into them. If it resisted the impact, they just rust-proofed the existing arms to prevent further corrosion. If they failed the test, it was a free replacement... More info here:
http://www.vosa.gov.uk/vosa/apps/rec...Text=Blank&tx=
https://www.scoobynet.com/scoobynet-...-imprezas.html