Haha, my team is going the opposite direction: we're leaving prometheus + grafana to datadog, and we're loving it. having every AWS monitoring default dashboard work right out of the bat is a bliss..
We just moved everything from datadog to Grafana, Prometheus and Loki, mainly due to cost. Honestly though, I feel like we get more out of the Grafana stack. Its powerful but simple enough to keep it pleasant to work with.
How about don't? Datadog offers everything that grafana does plus alerting, as well as more and better integrations (databases, AWS, middleware, etc...).
The cost aspect is one thing. Vendor lock-in another. Probably need to have a team that can lead the transition towards Grafana, educate and speak for it. Grafana has an enterprise plugin for datadog that potentially could ease the migration