According to the Rust team page Rust has not just one "Tech Lead" but 6 who have the responsibility of

    overall direction of the project, subteam leadership, 
    cross-cutting concerns

Which to means if a deadlock happens on a subteam these six will be breaking it.

Yet in general, consensus is the guiding mode of operation for all teams. The core team has never overridden a team's decision against their will, and while such a thing is technically possible, it would be considered a catastrophic event, I'd imagine.

(Source: I am one of those 8 (not six))