If I am in your case, I would:

1. Get the job. 400K would be quite a salary that would allow you to save.

2. AND Continue with your startup, by being on an advisory role. Delegate the business to someone you could trust (difficult, but possible). After office hours, you put in time to gauge how your startup venture is doing.

It is not quite easy to get a startup to a point where you are actually making solid progress. Of course, you would want to ensure your own survival as well.

Best of luck.