Is this sentence "We could quit now where we are a success" gramatically correct?
If "We could quit now where we are a success" is gramatically correct, then how to explain it?

Question

Answer

It is basically grammatically correct, except for a missing comma, but awkwardly worded.  It would be better said as:
We could quit now, while we are a success

In normal English, the popular phrase is:
Let's quit while we're ahead.
Let's quit now, while we're ahead
[Note where the comma is used]