Presumably, manually running builds locally is an automatic failsafe option if you have the same people around who originally set the build pipeline up in the first place.

In 2021, basic business continuity plans for software companies should incorporate these sorts of concerns. You should have a published procedure somewhere that a person could follow for producing the final build artifacts of your software on any machine once backups are made available. Situations like these are why I check in 100% of my dependencies to source control as well.