@HarjotDhillon You are correct that HCN is a weak acid. Therefore, the reaction itself will be slow without a catalyst. However to whatever extent, CN- WILL be generated and the pathway used will be a conventional substitution from the carbon end. AgCN will be extremely negligible to begin with. There is no real "blockage" to producing CN- ions with HCN as there is with AgCN. At best you can expect a mixture which will tend towards the nitrile as dissociation increases via thermodynamic control