The tracks are not fixed to the ground. If a train grips the tracks in order not to fall over, it will probably still fall over and also rip the tracks out of the railbed as it does so.
This is not always true, most of Shinkansen track is concrete slab track, which is effectively fixed to the ground. And they actually do have special anti derailment guides build into the track to prevent a train from derailing during an earthquake:
https://www.rtri.or.jp/eng/rd/seika/2006/01/safety_E05.html
True, as we've learned in this article. I guess it will have to grip to something else.
But in the theoretical banking the original comment was talking about (let's say 30 degrees), the track would probably have to be secured to the surface...
Well, how heavy is a bullet train, where is its center of gravity, and how much banking does it need if it wants to travel, say, 300 km/h in a (how sharp?) a curve?
Keep in mind that banking is only comfortable if you are traveling at the correct speed.
There are a whole host of reasons why a train may not travel at maximum speed for a given segment, and the rail line still needs to be reasonably comfortable at all of those.
