My Lawyer Left The Firm In The Middle Of My Case.... What Should I Do?

I was seriously injured in an auto accident so hired a law firm with great reviews (4.8 out of 5) to handle my personal injury case. The lawyer that was assigned to my case was the managing litigation attorney with nearly 20 years of litigating experience which was great. But suddenly he left the firm and they never bothered t tell me (until I asked to speak with him) and assigned an inexperienced associate attorney who just graduated a year ago to handle my complex case. Now I am worried that his obvious lack of experience will hurt my case since I heard insurance companies love to bully and lowball inexperienced attorneys.

The status of my case: at fault driver's insurance already accepted liability and paid policy limit. My treatments are nearly over after a year and cost nearly $100k which was covered entirely by Medpay. We are now pursuing UIM claim worth nearly half a mil and probably headed towards Arbitration.

I believe I had 3 options but not sure which one is best:

1. Follow my lawyer to his new firm which is one of the largest law firms but with horrendous reviews (1 out of 5). I would obviously request that only he handle my case and no one else so do bad reviews even matter?

2. Hire an entirely new firm with caveat that only their best and most experienced attorney handle my case. I would probably check their website to make sure no associate attorneys are on their staff.

3. Stay with my current firm and let the "kid" get his feet wet with my half a mil case? I mean they claim that a senior attorney will oversee his work but he says he will personally litigate if we go to arbitration which worries the hell out of me.

So what would you choose if you were in my case?

Location: CA