RGB Compressed ETC2 texture format

I have a question related to the RGB Compressed ETC2 and RGBA Compressed ASTC formats.
In the manual it states that on Android it is partially supported:

RGB Compressed ETC2 - Except on OpenGL ES 2.0; there ETC2 textures are decompressed into the ETC2 fallback format specified in the Android Build Settings or on the Android tab for the Platform-specific overrides.

RGBA Compressed ASTC - Requires Vulkan or GL_KHR_texture_compression_astc_ldr OpenGL ES extension.

In case some device doesn’t support Vulkan or GL_KHR_texture_compression_astc_ldr what happens? Will the application close? Will the image exhibit artifact? Will it be converted to some other supported standard format?

The same question follows for RGB Compressed ETC2