In theory if the company is not bankrupt and shares are still being purchased then price of going down won't cause any issue. However price going below in paise would be alarming. So in such case it'd be treated like penny stock. So it may not offer some strong funding from other financial ventures. In practice many companies go down in pennies or say paise cost. So it should not be a problem. But when it touches zero then in theory it is as good as low income company and shares won't get sold. New companies have such situation for decade in some cases. And unless they get developed into better corporations, the price of share won't be increases and often goes down.