Calvinists hold that you can't even believe until you are baptized, which means you for sure will not believe if you are not baptized and therefore will not be saved.
BTW, Matthew (27:44) and Mark (15:32) say that neither one of the thieves believed in Jesus. Luke says one did, 23:39-41, and John makes no mention of the thieves.
That is different from what you originally said =>
One cannot be saved without baptism.
The clergy consensus today, after I asked them to share their wisdom on this matter, was that we do not say that one cannot be saved without baptism.
It not only limits God's choices to a ritual here on earth, but it goes against the concept of perfect (divine) love.
And the final advice given was this - when in doubt about these things, always ask yourself, what choice would be made by a God of Perfect Love?