$50k/month comes out to $600k/year which is the cost around 2-3 engineers counting overhead.
To manage infrastructure at that scale themselves they'd need someone who knows DevOps. To write services at that scale they'd need someone who knows backend engineering and micro services. Then they'd need to be able to have 24/7 on call rotations for when things break. And of course, like any rewrite it seems like a "couple month" project until you get into the details and it becomes a two year project. Soon you've got a full 6+ person team and are paying them a lot more than $600k/year.
To manage infrastructure at that scale themselves they'd need someone who knows DevOps. To write services at that scale they'd need someone who knows backend engineering and micro services. Then they'd need to be able to have 24/7 on call rotations for when things break. And of course, like any rewrite it seems like a "couple month" project until you get into the details and it becomes a two year project. Soon you've got a full 6+ person team and are paying them a lot more than $600k/year.