What if Aurelian somehow survives the plot against him either someone catches on about the forged documents or has a change of heart and tattles to him what happens from there. Do you think he would have done well in Persia and how would Christianity fair given Aurelian's favour of the Sol Invictus Cult?
My guess is if he somehow survives this plot he will be killed in the next plot.
The situation with him was like with Julius Caesar - a brilliant general, able to defeat all his enemies on the field of battle but doomed to get assassinated.
Julius Caesar made way to Octavian Augustus. Aurelian made way to Diocletian.
But if he was lucky enough to live for a few more years, well, one thing for sure - Aurelian would not conquer Persia. Maybe he would defeat it, loot it, but he wouldn't annex any territory.
He was wise enough to let go of Dacia. So he had clear mind and understanding of limits of the Empire. Not to overstretch.
As for religion. Christianity won in a fair competition among all creeds in OTL. So it would do in this ATL, I think.