The real reason that people do not disconnect while on "vacation" is not because all the work is piling up. Most of the work piling up is not the really critical work. It is the routine stuff.
The real reason is that they are afraid the business can actually go on without them (as it should). Folks worry that they will not remain relevent and that if they can go away without being needed this somehow might mean they are not really that important. So their ego requires the constant contact and reminder that they are needed. CFO/COO/CEO the business will and must move forward. The rest of the folks are even less critcal so all will be fine while they take a break.