We know with absolute certainty that Baptism of Water does exist, whether deathbed or sooner.
Whether BoD does or does not exist is known with absolute certainty only by God (maybe by the angels and saints too) and of course by those particular affected souls at a point-of-no-return, as it were.
Note that I didn't claim that BoD does not exist. But as a baptized Catholic, of what business of mine is it to insist that it does? With regard to the souls of others, do I have the right to tell the unbaptized that it's no big deal, just be nice and all will be fine?
When considering points of contention w.r.t. the eternal teachings of the One True Faith, always ask cui bono, if only cui bono in this mortal life in this vale of tears. In that, the logic is unavoidable, and the honest answer might shock like a bucket of ice water.
So, I have said also that, at the very least, God has not revealed (directly) the existence of a BoD. Then, even if one could argue theologically in favor of a hypothetical BoD, there's no evidence that anyone has ever been saved by said BoD (no, the putative BoB incidents do not prove BoD).
But, as I have also said ... along the lines of a Pascal's wager scenario ... IF there's such a thing as a BoD, and God has willed to save some souls this way ... then my lack of belief in it means nothing, and would not have prevented that soul's salvation. Now, on the other hand, if there ISN'T a BoD, then some souls could easily be lost on account of BoD theory because it could lessen their zeal to receive the actual Sacrament of Baptism. How much more ardently would a soul desire the Sacrament if in fact he believed it was his only chance at salvation? On the other hand, could substituting the desire for Baptism with a desire for the desire for Baptism actually still "count" or would it ironically undermine the possibility of salvation by ACTUAL BoD.
Finally, without BoD, the modern heretical ecclesiology and soteriology, where Jews, Muslims, Hindus in Tibet, etc. can be saved ... would not be possible without being recognized as directly contradicting EENS dogma.
BoD has been used as THE weapon to gradually undermine EENS, lead to religious indifferentism, and lead to the Vatican II ecclesiology.
If I were elected Pope (or selected by God, that is), one of THE FIRST actions I would take would be to forbid all Catholics from ever mentioning BoD again, and I would require the addition to the Creeds, both the Nicene and the Apostles, a phrase or sentence affirming belief in Baptism, without which there can be no salvation. I would then pray and study about whether it needs to be condemned as grave error or possibly even heresy.