Assuming ring back on transfer is not enabled, after an unattended transfer, the person transferring the call is taken out of the loop, i.e. the call is treated as though the caller called the final party directly. Voicemail or follow-me for the recipient would determine where the call goes on busy and no answer.
If both voicemail and follow-me are not configured, the extension will ring until the ring timeout is met. Thereafter the call will be hung up.