We're told that it was going to be Wiglaf's first time as a fighter (lines 2626-2628), so of course there was the possibility that he would fail, or at least not come up to Beowulf's standards (who had a career of, what, 60+ years going for him?). But immediately after warning us that this was his first fight, the poet says,
"His spirit did not break and the ancestral blade
would keep its edge, as the dragon discovered
as soon as they came together in the combat."
So we know, even before the fight begins, that Wiglaf is going to be brave and that his sword would not fail him (double entendre, anyone??).
In addition, Wiglaf's speech to the shirkers (2633-2660) lets us know that he is definitely ready for the challenge that faces him. His loyalty to Beowulf, and his disgust at the men who won't go help him, is testimony to his strength of spirit and courage that will see him through the fight ahead.