Hi, MelRay!
I really don't think it's possible to "stretch" the audio" to match the length of the video(after you've deleted the affected portion of your audio track upon unlinking it from the video), the main reason for this is, in part because any speech would be out of synchronisation(severely so) with the mouth movements of anyone speking on that clip. Even if there's no-one speaking I don't think it's possible.
The best "trick" would be to leave the video and audio components linked, and at the adversely affected part of the audio, lay over a bit of music from the "Smartsound" library or one of your own audio pieces, or a piece of narration to "hide" the affected portion of the audo track.
Cheers!
Neil.