Sorry, am I reading this right? You replaced a service that required a team of five Erlang developers with an AWS offering for $1000/mo? Why wouldn't you do that regardless of the language involved?
This can't be 1 person anymore, what if they person takes a vacation. So that's 2 people. Perhaps the 2nd person can be much less capable that the first, they just need to hold the system together for how ever long it takes the lead dev to come back from his 2 week hiking trip in the amazon....yeah not good enough. So then you end up saying we actually need proper on call, so now you're hiring a team.
What if it was another language? Let's assume it's a core language of the organization. Then you don't need a team, but capable Sr/Staff Engineers who can jump in during emergencies. Might not be the perfect fix, but then you have a series of people who can duck tape it together until the person responsible is available.
Using Erlang tied our hands, and made a decision to throw a project business requirement.