A question that we should also think upon: Would Erwin have wanted Levi to turn him into a mindless Titan just so he could 'live'?
Remember that the Titan injection turned Armin into a Normal Titan, not a Titan shifter. He still needed to eat Bertolt afterwards. If both turned into Normal Titans, only one would still be able to inherit the Colossal Titan. There has been no precedence in the manga nor a mention of an event where two people inherited the same Titan powers but a person may acquire multiple Titan shifter abilities.
Besides, as seen in Chapter 84 and to quote from the wiki, Levi himself did not want to bring back Erwin, even if there was a way:
Levi notes that Erwin became a demon just as they had wished, and that he deserves to rest, rather than be brought back into their hellish world.
So, no, only one would still survive.