I just "getting captured" is a typical fudge for a lot of DMs: the DM wants the PCs to get captured. So the DM sends a capture group of bad guys of after the PCs. Then has a random wacky combat...where the PCs roll high and the DM has to fudge things so the PCs get caught.
If I want something to happen or not happen: it just does or does not. I don't leave things up to rolls unless I want too.
When I do roll dice, I let the dice roll as they may. Whatever is rolled, is what happens.
Well, "I" never want things that depend on rolling dice , but powerful NPC foe might want to capture the PCs for a reason, then that encounter would be a optimized capture group. So chances are the PCs would be captured, unless the players really paid attention, focused, worked together and made sure that did not happen. But if the PCs did win, it would not disrupt anything. Though if the PCs don't take any action the foe is likely to try again...maybe. Or maybe the foe would try something else.