Glowforge has records, logs and video captures of every print, and they use them to determine what caused the issue each time…they have always replaced warranty machines at their cost if there was a physical issue with a machine part. (They’re not exceptionally quick about it due to the current structure, and other world-wide system failures, but they are very fair and persistent.)
What this all means is…the offer that they gave you is in all probability the best one you will get from them. You can use that to make your decision as to what you want to do now.
I’m guessing you have a Pro model since they offered you a replacement for $4000, and that’s not a bad deal at all. But if you don’t have the money for it, you would need to consider your other options.
Reading through your other posts on the subject, you have another option that you might not have thought of…you can take the money that Glowforge refunded to you on your Extended Warranty purchase attempt and buy a cheaper laser. There would be a much smaller learning curve now that you know more about how a laser operates and you could use it to get back to business a lot more quickly.
Or maybe you could negotiate on a Basic model, if you want to stick with the Glowforge…if I were in the same position, I would ask them very nicely if they would consider a slight discount on the Basic instead of the Pro model. They’re very generous people, they might consider it. (You have nothing at all to lose by trying.)
The important thing for you is to get back to a position where you can start bringing in income again, because that’s the lifeblood of your business. (Once you have the Basic paid for from the business profits, you can look at getting a second one, or a Pro if you need it for larger jobs. Grow into it when you can…having a backup machine is critical for a small business, and nobody ever tells you that when you’re starting out.)
Setbacks unfortunately happen in every successful business, you pick yourself up, brush yourself off, and make a decision to go forward the best way that you can. When things are better, you can look back on the setbacks as a learning experience. (Although I do have to admit…they really do suck when they’re happening. ) 
Good luck with it!
