Agree with Oleksandr Kaleniuk’s comment.
Also, to add to it, code owners should be expected to grow more people to have proficiency with the code base they own via code reviews and design reviews. They should be encouraged to recognize people who have become experienced with the component and are contributing to it significantly by giving them ownership and delegating some code reviews and design reviews to them. They can be motivated to so by appreciating these qualities in performance reviews or through an incentive system.
Not only, does this solve the problem of “getting hit by a bus”, it gives experienced engineers more time to work on other things than the day to day churn by growing other engineers as code owners.