The errors won't be swallowed only in two cases: either if router.get actually supports promises (thus catches all the bubbled errors on its own) or if you have unhandledRejection global listener. Some node versions do show unhandled rejections automatically (e.g. v7.x), but that is getting deprecated soon.

So, there's quite a real risk of quiet failures in that bit of code.

Upd. Looks like even though the unhandled rejections warnings are getting deprecated, the rejections themselves will actually stop the code execution with non-zero exit code! Which means most of the issues I had with that code are gone (which is awesome)