The failure modes of rocket engines could be explosions but nobody says you can't have multiple redundant engines on a single rocket. In fact, in 2012 Falcon 9 demonstrated exactly that: one of their 9 Merlin engines blew up but the rest redistributed the load and the rocket successfully delivered the payload to the ISS[1].

[1] http://blogs.discovermagazine.com/badastronomy/2012/10/08/sp...