The other example we have of immortality in Harry Potter is Nicholas Flamel, who has just continued to live and live by using the Elixir of Life, brewed with the Philosopher's Stone:
The ancient study of alchemy is concerned with
making the Philosopher’s Stone, a legendary
substance with astonishing powers. The Stone
will transform any metal into pure gold. It also
produces the Elixir of Life, which will make
the drinker immortal.
There have been many reports of the Philosopher’s
Stone over the centuries, but the only Stone currently
in existence belongs to Mr Nicolas Flamel, the noted
alchemist and opera-lover. Mr Flamel, who
celebrated his six hundred and sixty-fifth birthday
last year, enjoys a quiet life in Devon with his wife,
Perenelle (six hundred and fifty-eight).
Philsopher's Stone - page 161 - Bloomsbury - chapter 13, Nicholas Flamel
This example seems to show that with the Elixir of Life a person just continues to get older and older. I cannot find any canon information that indicates struldbrug-like immortality. I think if Horcruxes offered struldbrug-like immortality they would have been less appealing to Voldemort as a means to immortality. Voldemort was controlling and arrogant. I think he would have disdained anything other than straight up immortality. Of course were a struldbrug-like method the only way of attaining immortality, I have no doubt that Voldemort would have utilized it. It would have been better than death.
On thing the bio on Nicholas Flamel doesn't tell us is whether Nicholas's body stopped aging when he first took the Elixer of Life. It seems logical that physical aging was slowed or went into some kind of stasis that was sustained by the Elixir of Life.