If Sirius had lived to HBP, I’m pretty sure it would have gone something like this:
Dumbledore: Okay so I’m going to take your underage godson on a dangerous, possibly deadly mission to destroy Voldemort’s soul.
Sirius: *Bursts into castle, slings Harry over his shoulder*
Sirius: THIS IS A WHOLE BUNCH OF NOPE, HARRY-JAMES. WE’RE GOING TO SWITZERLAND. TIME TO LEARN GERMAN OR W/E.