Dying hair dark auburn?

I have darker tinted brown hair and i'm wanting to dye it dark auburn in a couple months. I'm wondering if when the auburn starts to fade will it just wash out and gradually blend back into my natural hair color, or will roots be an issue?

I figured since its dark auburn that the roots wouldn't be too bad because my hair is brown anyways, but i'm not sure.

Both of my sisters are hairdressers but they seem to get annoyed when I ask anything so I came here instead.

Thanks!