Board Thread:Lore Discussion/@comment-24443955-20140120081548/@comment-16047389-20140120153554

Arniel Gane didn't really "return" though. He is at best stuck between dimensions and at worst dead. There's also no real evidence that he even went to the same location as the Dwemer, since he used a Warped Soul Gem instead of the actual Heart of Lorkhan, and also used a time-worn Keening.

Falion, on the other hand, may have met Dwemer in Oblivion, but I don't think that means that the Dwemer were sent to Oblivion. It's possible that the Dwemer he met are just individuals that got trapped or chose to stay in different realms of Oblivion, as some mortals often do, and therefore were simply beyond the Heart's effects.