It would depend on the level of communication/or closeness you have with your family or those you're close to.
Personally, i'm an advocate of just disappearing, but it requires elaborate ground work, such as limiting or distancing one's self for a set period of time before the act, or making people think not hearing/knowing about you is something that's normal.
This has taken me a long time to achieve and personally, im quite happy about it. However, if you do prefer to just fade away and disappear, you have to factor that in to your CTB method too, as these people would definitely have to deal with the aftermath when you're eventually found.
I think the cases for saying goodbye/closures are important are based off of case studies/instances wherein the focus was on the ones left behind, but no case studies exist (as far as I know of) where the family or those that were left behind were doing...ok? hence the generally leaning towards the need for closure.
on a more logical level, i find it difficult? i guess to understand the value of closure when I think about it. Every person has something or the other that they have to worry about. Money, health, constant bombardment of social media, etc. I highly doubt my passing would actually make a dent, regardless if they knew it or not. But that's just me.