Now, will we always be able to use template literals, or will there be times that we will have to concatenate strings?

There are still environments out there which don't support template strings. The number of those environments is shrinking drastically - but they do still exist.

When you use something like Typescript or Babel to convert your up to date, full features javascript to a target platform (transpiling), you can tell it what version of the ECMAScript (aka JavaScript) standard you want to target.

At that point, you can still use template strings, and the transpiler will handle converting that into string concatenation for you. So that environments that won't understand the backtick can still work.

A great site to check whether a feature of HTML, CSS or JavaScript can be used in your target environment is "can I use": https://caniuse.com/template-literals - this will tell you whether or not you should use string concatenation.