He said universe not just guardians. I doubt he'd be able to figure out the vault of glass by himself. Yeah atheon can teleport him and he can use instant transmission to get himself back, but unless he takes the relic with him, which I doubt he would, he's done.
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He could instant transmission to the relic and get it
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He doesn't know what it is. He has no one to assist him. Plus its a different time, so he's stuck and going blind in the past. Whether he destroys the oracles (doesn't know what those are either) or not he still can't make it back.