It's far more than a record keeping system, and integrating a rating engine and billing system into a cellular network with millions of transactions matched up to millions of subscribers per second in real time is not trivial. R&D is requried to keep them ahead of the competition...they need new products and innovations.
As for the brains of the company being gone, I have seen nothing to indicate this. Lucas and Vishal have been removed from the technical details of their products for years. As long as they take care of the best developers they have, they'll be fine in that regard.
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I am not saying it is or is not. What it is is an uncertainty.
Everyone saw what happened to Apple when they got rid of Jobs who had left development long ago.
It is not about developing products it is the vision one has for the products.
Like Lucas was not a businessman a businessman will never be an innovator.
https://stripe.com/about
This company has jst been valued in the billions with a round a funding.
Good luck getting us to hand over another 60 million with those perfs in the way.