Webm shows a pretty extreme example of a solid carbide tool not snapping. This is also what you get when management overloads your shop's programmer. Then management subsequently has to subcontract out a program the subcontractor thinks slotting with a 1/8th endmill 2" long in 0.025" DOC steps is a good idea. The part is also stupid because why would you need spigots like that, but that's another rant entirely.
When doing something like this, the correct way would be plunge roughing in % of tool radius step-overs (% would have to be whatever step-over is easiest on the tool, anywhere from 25% to 75%); once the material is out of the way, you clean up the scallops using the side of the endmill without much problem. You can easily machine with an endmill that long if you're taking 0.010" or so on the tool's flutes from the sides, and very little if any on the bottom of the flutes, even if your depth of cut is large. Slotting with an endmill that long is how you push carbide "brittleness" to it's maximum. It's just a terrible idea in general.
That could probably happen, but from my experience with carbide tools, they're brittle, but not as brittle as some would imagine. They're even less brittle when "supported" by steel somehow.
When dropping a solid carbide tool, it's much more likely to chip locally at the impact point than break completely like dropping a glass bottle. Yes, carbide is more brittle than steel, but "more brittle" is relative. All carbides are not the same, and all carbides (even from the same company) can have their blends of 11 herbs and spices for whatever purpose they need, with a bajillion coating types and blends on top of it all.
I'd use regular carbide tool methods, the wheel is already invented and making a good carbide thing is not really hobbyist friendly. Manufacturers can make a 0.015" diameter solid carbide twist drill with coolant holes twisting down inside the flutes (I'll get a picture, we have some at work, and microscopes to be able to see the coolant holes too), they can probably make a rifle barrel. They'd probably need the mandrel like hammer-forged barrels, but beyond that it would be their usual carbide production space magic.