The future of htmlimport - will my app stop working in 2019?

There is a warning shown in my Chrome 70 browser’s developer tools console:

[Deprecation]
 HTML Imports is deprecated and will be removed in M73, around March 2019. Please use ES modules instead. See https://www.chromestatus.com/features/5144752345317376 for more details.

Will my vaadin flow application stop working because using the @HtmlImport(...) annotation?

Your Flow app will continue to work but will use a polyfill for the HTML imports in Chrome also (it does that in other browsers today already)