Probably need to expand on the question a bit so we can provide a more accurate answer. Are we talking about OOC or IC dislike? How are they disliked? How are they crucial to the plot? Are they a a character you can modify?

So I had this one character ages ago that I created who had a bubbly personality in a post apocalypse world. After a while I really disliked the character so I ended up dropping them into a tragic incident and stepped away from the RP. Months later the RP was rebooted and I was asked to return. I came back, created a new character and was asked, "what about this one you had before?" because technically she was still alive.

And this is when the real fun began...

I chopped off her arm and took out her eye, replacing them with cybernetic alternatives. Destroyed her bubbly personality, replacing it with depression and sadness. Then finslly gave her PTSD as well as a psychosis problem, all thanks to an introduced plot element as well.

Basically, killing a character isn't always the only option. What you might need to do is find that trait or attribute that you don't like and see why its conflicting in the story or the character development.

Your plot also doesn't have to be so rigid as well. Its hard to tell without knowing, but things do fuck up sometimes in their adventures. Protecting them can be classified under the term of plot armour. Its not a bad term as a lot of characters in movies like Marvel have heavy plot armour, but you compare that to game of thones where main characters are killed, and you'll see how a lack of plot armour can be a good thing.