Yes. Natsu can tap into his etherious mode, But not whenever. We caught a glimpse at his etherious mode in Fairytail: Dragon's Cry. He was only able to trigger this mode whenever he felt a strong wave of emotion. In the manga series he triggered his etherious mode after seeing (what I can presume as an illusion) of Lucy dying. The anime series hid this mode when future Lucy died (Episode 194-198.) He can also still use his Fire Dragon King Mode, but as he said in the manga, He will use the power given to him by Igneel. He was able to use his mode again without Igneel's power but the results weren't the same. All in All, Yes he can still use both modes, but he needs to obtain that power to activate them by himself (half the way there; already can activate FDKM)