It depends. The insurer may still be willing to settle. Sometimes, once the insurer committs to trial settlement offers are withdrawn. Other times the insurer will still be willing to settle.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.
Only one way to find out - ask the insurance carrier (or its attorney) who offered the settlement if it's still on the table. There is no legal obligation for the offer to remain open (unless it was specifically conveyed with a condition that it was to remain open for a certain period of time), but many offers stay open indefinitely.
A case can settle at any time. You've heard the expression that a case settled "on the court house steps." That means it settled as the parties were walking into the court house to go to trial.
Whether or not you can still settle the case depends on whether or not the other side still wants to settle. Normally they do want to settle. Technically, once you reject an offer, it is off the table but very few insurance companies hold to that. Call them and ask. The worst that can happen is that they will say "No."
As a matter of contract law, which offer and acceptance boils down to in legal terms, once an offer is rejected by the other party, the offering party has no legal obligation to maintain its offer. Many insurance carriers or third party administrators add a deadline to an offer, but as a practical matter insurance companies are under great pressure to settle claims and close files and it is doubtful that the offer will be permanently rescinded. Also, judges in the workers' comp system in California have heavy caseloads and will often push a defendant to renew its settlement offer once the trial judge finds out that the claimant will now accept such. Remember that a case can settle at ANY time, before, during, or even after trial. If the judge finds that the settlement offer is adequate, the judge will approve such. As the above answer notes, many cases settle on the day of trial. Be aware however that if the defendant discovers new facts (prior claims, surveillance video, etc.) that changes the situation, the defendant may rescind its offer based upon the new circumstances. Some cases increase their value with time, just like fine wine, while others decrease in value, like expired coupons. If you have an attorney experienced in workers' comp matters, follow his or her advise. If you must go to trial, you will do much better with an attorney, Good luck with your decision.