Happy to help
You fractured your neck, check with your consultant or GP but I wouldn't carry a rucksack with a laptop in it of anything solid with sharp corners
All that my consultant said was "no contact sports for a year." He said he was confident that if I came off my bike again, my injury is now healed enough that he's not concerned that I would be at any additional risk (this was about 8 months ago).
I tried with the rucksack and with the panniers, and I like the rucksack better for a couple of reasons: my panniers aren't very big, which means I always need both. Most panniers I've seen aren't suitable for carrying around when
off of the bike, which matters when going to the shops. They have nowhere to store a helmet.
The last time I rode with my panniers, I believed they were water resistant to the point that they were safe to use in the rain. They were certainly sold as such. When I got home, there was a puddle in the bottom of each, and I had a laptop in there.
Suffice it to say that I've got the choice of buying a rack and panniers or a rucksack, and I've been enjoying the rucksack more lately.
I'm now down to a choice between the Deuter Giga Bike and the Osprey Momentum 30. I looked for roll-top waterproof packs, but none of them had anywhere near the feature set of those two bags.