What to do with a bent but not broken aluminum seat stay
Aluminum alloy is weakened by being bent. The seat-stay is bowed in so that loads will tend to bend the stay more. The stay probably will not fail suddenly, but it will develop a crack where it's bent if you keep riding it.

It's probably OK to ride on temporarily, even if the stay does fail the other stay will support the wheel. 

You say the bike is a Cube so presumably you are in Europe. The driver's insurance will cover the damage done to the bike, or you can sue the driver in some sort of small-claims court.