Jokes aside Mihawk is safe, as irrelevant as he is and always will be to the overarching plot, Oda has simply had him in his backpocket for when he needs to fight Zoro. When that time comes his feats will speak for themselves. I don't expect Mihawk to be anything more than what Oda has been telling me he is for the past 20 years, just someone really really strong that Zoro will fight someday, so there's no need for disappointment. Good design, and badass feats is all his character needs, only problem is we will have to wait forever for him to receive them because like I said, Oda doesn't even see Mihawk, he's not in his thoughts, or notes, or any of that stuff. He's just sitting on the shelf waiting for that moment, all cause he is linked to Zoro, not Luffy.
Kizaru is more expendable because there are others who share his rank...I was always afraid of the possibility of him not being allowed to go all out. The clock is ticking.