The concept of zero (as a number) is not necessary for positional notation, one can do with a placeholder symbol, used like a punctuation mark, or even with just a blank space. This is exactly what Sumerians and Babylonians did in their sexagesimal system of numerals since 3rd millenium BC, the earliest known positional system. This system was later transmitted to Hellenistic Greece in late 3rd or second century BC, and was adopted by Greek astronomers including Hipparchus for their calculations. Ptolemy uses the placeholder symbol in his Almagest, it looks like letter o (one speculation is that it stood for "obol", a coin of smallest value). But as MacTutor in its History of Zero writes "one might be tempted to believe that at least zero as an empty place holder had firmly arrived. This, however, is far from what happened. Only a few exceptional astronomers used the notation and it would fall out of use several more times before finally establishing itself". You can see placeholders in the sexagesimal and some other historical positional systems in Has a digit ever been used to represent the number "10"?
Indians most likely encountered the sexagesimal system in their contacts with the Hellenistic world, although there is no direct evidence of transmission. Around 500 AD Aryabhata used a decimal positional system without even a placeholder zero, and some other Indian manuscripts used a dot as a placeholder. Aryabhata's word "kha" for the blank will later be used as the name for zero. But by the time Brahmagupta started talking about zero as a number over a century later positional notation was already established for millenia. I am not aware of any place where the development went the other way, from number zero to positional notation. Zero number appears to be a far more challenging concept than a punctuation mark.