It looks like your lawyer has investigated this in detail. Given your lawyer’s professional expertise and experience, we’d recommend you take their advice and review the options. We use lawyers ourselves for situations like this, and we always follow their professional guidance.
All in all, though, we know how devasting this is for you, and we are truly sorry that a patent issue has arisen for you, especially after so many successful years of selling this product. I think now, is the opportunity to review if you wish and have the confidence to fight the legal battle or withdraw the product. Only you can decide this, with counsel from your lawyer, the path you should go down.