Be careful of reusing code if you've exited though.

But taking a concept with which you're familiar and building it out for a new purpose should be a good short-term approach if you're able to pull it off. You've got $60k, which is a good sum which gives you a nice chunk of time making it easier to earn the next $60k, which makes it easier to earn the next $120k.

So you earned a good years salary, in under half a year, with knowledge to apply in new projects.

Is there another business opportunity in your client's industry, or another industry with which to apply similar toolsets you just created? You have the luxury of a bit of time to make a decision.