If an error has occurred while having transaction, what will happen to your BTC?

[CoPil]

For example, if you are buying stuff online using your Bitcoin, then an error has occurred (like network error, something like that) will your Bitcoins vanish?  Or will they be safe? 

[karmakeddon]

Most likely, if your transaction got sent before the network error happened, there would be a searchable transaction ID for it. I suggest you go to blockchain.info and enter your wallet address. Try to see if there is a transaction that coincides with the time of you placing your order.

Otherwise, if the transaction was not signed and sent, the funds will stay in your own wallet.