In terms of difficulty, it's far easier to make a sealed case water resistant than it is to make one that opens up and has a gasket to fill in the gaps around the openings. That means you're not likely to get both water resistance and a removable battery in the same phone. Not impossible, but as demand for removable batteries isn't super high, the cheapest and easiest way to do it is seal the whole thing up. Looking at the engineering that went into the S7's micro-SD card slot, I can see why they're going to sealed phones.(Google it and look at the images for a quick understanding.)
As for the cold water cycle, my S7 would have a shot at surviving it, as would a lot of the other water resistant phones. It's pressure rated for 5' of immersion for half an hour, so there's a good chance that it could make it through that. The impacts would be the biggest concern. Even if most of them were against wet clothes, all it would take is one good shock.
In terms of the removable battery, the S4 batteries were so shit I was swapping a new one in every day or two, despite charging at both home and work. With the S7 I've run it dead only 2x since I got it, both times in the car on long drives. At some point I should get a car charger to fix that problem....But it really is far more energy efficient, and the battery is far better than the S4. So far, I don't miss swapping batteries all the time. Depending on how the battery ages, that opinion may change.