Yeah, pistols as back-up is how pirates usually did it. That said, if you're in any sort of melee, reloading a musket is going to be pretty much impossible. There's like eight steps you have to do in order. There's a reason that even up to the Civil War, after a couple volleys it was 'fix bayonets' and into melee.
If you're going for any kind of realism, then honestly, I'd say a musket user gets his one shot off at the start of combat then has to melee or go to pre-loaded pistols.