Janeway's log notes that "most" of their Borg implants have been removed. Would they still not need to regenerate like Seven and Ichib after they were assimilated?
Seven (and the children) still need to regenerate because their brains still contain Borg implants whereas Janeway, Tuvok and Torres' implants were (eventually) entirely removed.
The EMH was (in VOY: The Gift) able to remove "eighty two percent" of Seven's Borg implants. The remaining ones were "stable" and she seems reluctant to have any additional modifications, believing that it would lessen her perfection.
EMH: I've extracted eighty two percent of the Borg hardware. The remaining bio-implants are stable, and better than anything I could synthesise at such short notice.
SEVEN: It is acceptable.
As we see in VOY: Imperfection, these additional implants (critically the 'Cortical Node') are directly responsible for allowing Seven and the children to regenerate effectively and that removing them is a non-essential and carries a strong risk of death. Icheb notes that due to his young age, he can use a genetic patch to prevent a malfunction in his systems if he removes his node, but it's still a big ask and could easily have killed him.
EMH: What about you? Without a cortical node, how will you regulate your implants?
ICHEB: You should be able to compensate with genetic resequencing. This isn't suicide, Doctor. I believe it can work. All I ask is that you consider it.
By comparison, Janeway and the crew were inoculated against Borg nanoprobes, preventing them from overriding key areas of the brain. The implants themselves appear to have been able to be removed in their entirety after their adventure, obviating the need for them to regenerate.
Just as the Borg Cube explodes, Harry Kim manages to beam Janeway, Tuvok and Torres back to Voyager where they can be relieved of their Borg implants.