In some specific places, yup:
- The
autofocus
attribute is specifically designed to replace a common JavaScript pattern
- CSS3 animations can replace JavaScript animations, so if we’re talking about HTML5 in the expanded Apple sense of the word, yup
But in general, I can’t see HTML5 diminishing the usefulness of JavaScript, nor frameworks like jQuery, one bit. Given that HTML’s development is constrained by browser releases, the best it can do provide markup alternatives to a few very common scripting patterns. Scripting is useful because it lets you do anything you can imagine, including things specific to the project you’re working on.
So learn away.