In reply to Matt.

Widgets aren't being deprecated yet. In any case, when widgets do transition over to blocks, there is a gallery block in Gutenberg for the gallery widget to transition to. In the same way, a Custom HTML widget was introduced in 4.8.1 and there is a Custom HTML block in Gutenberg. When widgets do transition over to using blocks, users shouldn't actually perceive any fundamental change in this regard: they'll continue being able to use images, video, audio, galleries, custom HTML and other widgets in their sidebars as well as being able to use such widgets (blocks) for the first time in the content of their posts as well.