Interesting how you tell us that by virtue of baptism we are joined.... The word baptizo, where we get the word Baptism, from the greek means "to immerse, submerge; to make whelmed (i.e. fully wet);". My wife is a former Catholic and we attended Catholic services for quite a while. We never saw any baptism that involved anything other than a little water over the head.... No submerging or making anyone fully wet....
Our Church discribes baptism as an outward symbol of our accepting Christ as our savior, just as a wedding ring shows I am married to my wife. If I didn't have a wedding ring, I would still be married to my wife (of course if I didn't wear my ring, my wife may have a few choice words about it, but she wouldn't divorce me either).
Matthew 28:19 informs us that we should be baptized, but baptism itself does not bring salvation. Accepting Christ does this, and only through Christ will we find salvation. One who choses to not be baptised may find themselves in a bit of hot water when facing Christ, but failing to be baptised will not prevent their salvation.
I have a friend who just recently accepted Christ as her savior. Other than a few Christmas services, she has not been a regular attendee at any church. She is now looking for a churhc to join. Of course she has been invited to mine, but other friends have also invited her to visit their church. She plans to be baptised, but should she die before she should join a church and be baptised, I doubt that she will get the "Go to Hell" card simply because she was not baptised.
Her soul would be "Baptised by desire" and she would be cleansed. Baptism is a normal requirement for entry into God's family. But, like the thief on the cross, or the situation where you're hit by a bus on the way to get Baptised, God provides.
SD