Christ set the example, so we should be baptized! However, if there is a situation that prevents someone from being baptized--such as when Christ was on the cross, and he was talking with one of the thieves. He told the thief that today he would be in paradise with him.
That man had never been baptized, and of course he couldn't come off the cross to be baptized, but Jesus never mentioned anything about it.
So, if for example, someone on their dying bed accepts Christ, but hasn't been baptized--then I don't think it would prevent salvation. But, if you can, you should be baptized!