Listen, there's a whole other thing going on here, too. He's playing a guitar with a floating trem system. The bridge (the mechanism the strings slot into on the body end of the guitar) is held in place by springs in the back of the guitar that balance the tension of the strings, and the guitarist can use the whammy bar to stretch or relax those strings, thereby changing the string tension and bending notes. It's a finely balanced system that's easy to throw out of whack.

Blowing a string on a floating bridge guitar lowers the tension on the whole neck, the springs in the back cavity pull a little tighter, and the whole guitar goes out of tune instantly. The moment you lose a string, you can't trust your guitar is in tune, and each string might go out of tune by different amounts. It's a mess.

Stevie shifts immediately into phrases and riffs that don't require perfect tuning (that big tremolo wobble at 2:38), and you can sort of hear him testing out the tuning of the strings, bending them where necessary to get them back in tune, etc. I only hear one out of tune note, and that's when he ends up down on the open D (well Db probably) string, which because it's open, he can't do anything about.

If you're not a guitarist, you probably don't notice that aspect of what's going on there, but it's a whole level of challenge above and beyond the guitar swap choreography.