So like the previous tes games I've gotten a case of the I must collect everything I'm currently after Dragon Priest Masks and just realized I never got he one before you fight Aldiun I ran from the Priest there as I didn't realize what he was and kept getting oneshotted... So it appears I not only lost that mask but also all hope of getting the secret mask.... I'm on 360 is there anyway to get back there or am screwed.

Sadly...You're screwed. Unless you load an older save, there's no way to get back to the Eyrie after you jump into the Sovngarde vortex. You can summon Ohdaviing for battle assistance with a shout, but outside of the cutscene, he's never gonna let you get on his back and fly you back up there again.

Hate to be the bearer of bad news, but if you're dead-set on mask collection, it looks like it may be time to backtrack.