None of these scenarios are insurmountable.
How are they going to handle snow? Sure most will have winter tires, at least in this neck of the wood, but I find you need the right touch now and then in bad conditions. I'm sure the self driving car will recognize it's snowing and/or the roads are slippery, but does that mean it's going to slow down to half the speed limit? Will the self driving car be too "confident" and zip along at normal speed, and hit that patch of black ice and end up in the ditch? Either way, overall better than human drivers I guess.
Electronic stability control on high end cars is currently better in maintaining traction on snow/icy roads than the majority of drivers. Combine this with a sensible AI and I'm sure it'd be better than 95% of drivers in snowy conditions.
Very random and low frequency situation: What if you're in an active shooter situation as your car is slowly navigating a parking lot, and you just happen to be heading at the shooter at low speed? I guess you just duck and hope for the best? I highly doubt there is going to be a "Warp factor 10 Mr Sulu!" button to get out of nasty situations.
The autonomous cars are always connected. As soon as the shooting has been reported, they'll know about it. If your destination is within say 3 miles of the reported incident, the car will inform you and ask for an alternative destination.
If the incident has not yet been reported, the on-board cameras and microphones can likely detect an armed civilian, and will automatically move out of the area to a safe distance, and will call in the incident at the same time.
If the incident has not yet been reported and the car doesn't detect it but you do, you can either hit a panic button or tell the car with your voice it's an emergency, it will then move out of the area to a safe distance, and will connect you to 911.
Similar scenario, what if you are approaching a 4 way stop and it appears the guy behind you isn't going to stop, and is going to rear end you? If you had control, you could slow down to 20 KM/h and proceed if no other cars are present, would the self driving car do the same?
The autonomous car will be aware of surrounding vehicles. It'll take controlled measures to minimize impact. This could be applying the breaks to ensure you don't get shunted into intersection traffic, change lane, or pull over. Pre arm air bags ready for instant deployment. etc.
Eventually the non autonomous vehicles will be banned, and this issue won't arise.
There will be some teething issues, but they'll get sorted pretty quickly thanks in-house simulators (that enable manufacturers to recreate incidents and run to millions of variables for the AI to find the best outcomes, this already exists today). Once resolved satisfactory the updates will roll out to all the autonomous vehicles thanks to being always connected cars.