FYI, the only car in LFS with a sequential gearbox + paddles is the BF1, all other sequentially shifted cars are actually simulating a sequential gearstick, where it is impossible to engage both the up and downshift at the same time.
Real race cars with sequential transmissions do not allow you to downshift past 1st gear. You always have to pull a lever or push a button or pull a cord for neutral. Same for road cars. Sometimes it's pulling both paddles (really bad idea IMO), but most modern sequentials have a stick on the center console that has a neutral setting just like an auto box.
I always try to put the car in neutral when I spin in LFS. I would like a neutral button of some kind. Though, if I had a clutch pedal I'd just use that.
If you have a accident when you are in 6th gear (over 200kmph), you don't need to get back to first gear, you need to get back to the pits in the Shift+P way.