Author's Note: For those who already read Watership Down Miniseries Remake: Necklace of El-Ahrairah and seen the actual miniseries, I wanted to answer the question to The Sapphire One. How would have things been different had Kevin gone with Bigwig? Especially with Nettle and Thethuthinnang? Depends... if you meant by if Kevin traveled to Efrafa for the first time with Bigwig... or being recaptured, while Bigwig still pretends to be a hlessi?
Also for your version, that's an interesting relationship as good friends and mentor. That'll be very interesting to see how it turns out. I liked the second choice because it comes out in a surprise and loved the idea to find him after the battle. Absolutely agreed to have his ghost/spirit visit the warren.