I think you mean to ask about ejabberd, and not Erlang, which is the language that ejabberd is implemented in.
My recommendation would be to go ahead with ejabberd since you are already using it (as I can construe from your question and my consequent assumption), and you must be quite comfortable with it by now. Of course, its raw speed and bug-free scalability definitely help.
Once you are in production with several thousands (or even more) users, and then feel the need to get into its innards, I would suggest that you take a week-long sabbatical from your schedule and get around to learning Erlang.
Original post: https://www.quora.com/How-far-can-you-go-using-an-XMPP-server-in-production-without-knowing-erlang/answer/Najeeb-Shaikh