I was going to quote the math at you, but amusingly enough you were the one who did it:
The time for hoping that a lucky roll will heal you is past once you've received two strikes, because then you could very well die on your next round and that's obviously a crappy and terrible outcome. Assuming you're always bailed out (if necessary) once you've received two strikes, this is mathematically identical to starting out down one strike, so we'll be using the "1 Strike" line. While the probability of getting that 25% recovery here is certainly less, it means that all potential losses are in terms of healing resources, rather than your death.
By that line, falling onto your sword and hoping to heal up some via rolling a 20 rather than relying purely on the party healer will cause you to need to be healed up from zero hit points 81% of the time, and from 25% of your maximum hit points 19% of the time. I think that, as 19% of 25% is 4.5%, that's the break-even point below which it becomes worth it to attempt to heal yourself through falling on your sword. Likewise, since a Cure Minor Wounds would only restore you to 1 HP, it's far better used by a Cleric to try and get you that 25% boost than spending all of them for the day on healing 6 HP.
Of course, in a time-limited situation (i.e. combat), or given the presence of unlimited healing resources, there's no point to ever doing this.